ok.., you may need to read these as a whole response (and not in isolation) as one point qualifies another in parts.

Explain more for my understanding: you are saying that by UK and EU law, your hardware and software is "theoretically" guaranteed for 6 years which equates to what the UK and EU consider the lifetime of the purchased system....
I only mentioned hardware in my post and only mused about the software. However, the Law states that "if it [product] becomes defective, or does not conform with the contract of sale”, a claim can be made under UK Consumer Law, for repair. This is in place for 6 years from purchase.
Basic and simplified Apple version here:
http://www.apple.com/uk/legal/statutory-warranty/
Arguably a system not functioning due to a [forced] software update required and provided by the Manufacturer rendering a system inoperable, or that it "does not conform with the contract of sale”, is a possible case IMO. I have never tried it on that basis alone, as I have not had a case so bad that could be proven. My 4S came close...
But of course (correct me of course if I misunderstand)....it is guaranteed to be "fully functioning" as per the day you purchased it, as as far as what Apple "guarantees" or says at that time is a "fully functional" OS X and computer for the time it is released.
Yes, sort of...
It must
"conform with the contract of sale”, so yes it must work as designed to work in it’s life time, not related to wear-and-tear, or user maintenance / treatment issues.
What happens
when you upgrade to a new OS (they say is compatible)
and they do not allow you to downgrade that OS when your system say’s it is not to the factory, or version it worked properly previously..?
Also Apple does not say that a product will breakdown after 5 years, only that is becomes unsupported. That is important to note.
Laws cannot guarantee that the OS X will fully function without bugs, let alone function together with third party software or hardware, even if your software and third party hardware worked on the old OSX if you upgraded of the life of the purchase. Who is smoking what in the courts of the U.K.?
Again, it must
"conform with the contract of sale”, so yes it must work at designed to work in it’s life time, not related to wear-and-tear, or user maintenance / treatment issues. So if you have a bike and the tyres wear out and the brakes fail, then you cannot really prove it was a manufacturing fault. If you own a completely sealed iPhone with no user maintainable parts and it is clear it has not taken any exterior damage / internal damage, then this cannot be argued against if a phone dies after 18 months.
So nobody gets to smoke anything in Court...

I have used this law twice with Apple and once with Argos (for a plasma TV 3 months out of a 1 year warranty) and never gone to court, they capitulate as it is not worth their while. I had an MBA replaced after about 4 1/2 years (hinge gate) and my iPhone 6 (bought September 2014) that died over the New year and was replaced under ‘Apple Care’ even though I did not purchase Apple care... They only have to repair under the Law, but as we know, they really do not bother, as it is not worth the time and money.
I was not referring to the actual system (hardware and software that is considered "the one purchase" as the law "suggests" as guaranteed. Of course the software that comes with the OS X like GarageBand and a few other software should work because it came with your purchase of the Mac and is considered "the purchase", but laws cannot guarantee that outside Apple third party software will work after the new OS X comes out for 6 years or the life of your purchase. Dream on....
I cannot qualify this for third party Software, but the system software provided with SL. For example, what happens when you need to update the firmware on your smart TV under warranty and the screen goes black and never works again. Do you just buy another and say, the TV was under warranty, but not the software…?
What I was talking about is that if you either upgrade or buy a new system with the new OS X, then try to use already owned software and hardware that is not Apple's (like musical interfaces let's say) that you bought prior to the new "guaranteed" purchase, and now does not work because of the once a year OS X change... Your screwed. No laws can garrentee that. Yes, you can downgrade to the older OS X if you upgraded, but if you had to buy a new computer with the next OS X, you cannot go back to a working OS X to use with your previous purchased software and third party hardware and have to purchase all over again (screwed).
Again, I am not talking about third party software. Also Apple has pretty much has done away with allowing you to easily downgrade the OS after ML. So you cannot always downgrade, unless you know what you are doing and pre-prepared a cloned [bootable] back-up. The average users will not do that. That is my point.
Snow Leopard concept is "liked" because finally an OS X "basically" worked and at the time Apple's goal was to worked hard to try to make that a reality. Now...no or maybe a little. At that time the war with Microsoft was on (remember the "I'm a Mac" videos?") Snow Leopard contributed to Microsoft's decline because Snow Leopard (after a few versions updates) "just worked". Many users at the time exodus out of the mess of Windows and into Apple's pie along with the success of the iphone and iPad.
Logic is not illogical says Spock...Facts are facts..

Apple needs to have a solid OS if they are still in the computer business or Microsoft "might" come back in the OS segment...again..
Snow Leopard concept is key for the future of OS X if it has one.
I liked SL because of mail, and could still use Quark 6 and other programs I use infrequently enough to not need to justify upgrading.
Microsoft will never come back (at least for me), because Apple will always just do enough to stay ahead. That is their business model.