Exactly. People kinda forget that one big reason Windows is a monstrosity is because they kept trying to keep giant piles of legacy code in there so people running old toasters with broken third party software could still use it.
IMO what Apple should do, rather than putting updates that mess with old systems, is just make the generational cutoff for updates more like... 2. So this go-round the 5 would be the oldest phone that gets new versions, and so forth.
With you on that call!
Yes, and 4S users should be able to downgrade to iOS 7.1.2; 4 users to iOS 6.1.3 if so desired.
Will ensure that a device will only have what it is capable of and no baggage from previous generations.
Although if you know what to do within Windows XP, I know you can surgically remove 80% of legacy support/ drivers, for instance 3 1/2" floppy drives/ 28.8k & 56k modems etc.. from the OS to suite your hardware, leaving a quicker OS.
Which was why Windows XP was so much in favour of the end-users until the implementation of vista and windows 8 <back on topic>