The only reason I can see would be that if a component didn't exist at the time of the previous release of the OS it wouldn't have driver support and some things might not work. The new MacBook Air's have the Intel 3000 graphics in them....they probably won't run on Leopard.
Research. The 2011 MacBook Pros all use the Intel HD 3000 chip in addition to the AMD chip.
People...from a hardware perspective - and I speak as a hardware guy - there is NOTHING inside the Air that prevents it from running Snow Leopard. I know what their "policy" says, and I'm against it. For all the guff Microsoft gets, if you want to run XP, they really don't care, because it's still supported. Snow Leopard, to my knowledge, is still a supported OS. Therefore, why can I not load it on a machine that should functionally run it?
Now, the ONLY thing I can think of is the Bluetooth 4.0 chip. That's specific to the Air.
As far as the scrolling, I don't want to have to be forced to set my machine back the way it's always been due to a change that wasn't necessary. We're not talking about some change for the better. We're talking about an option that should NOT be default, but still disclosed.
I like my Dock on the left side. Why? It gives me more bottom real estate. Can you imagine how many people would be bothered by Apple suddenly saying that the Dock can no longer be moved from the bottom OR resized? Change for the hell of it. There will always be those who just bow down to every pointless change Apple makes, of course, but the issue here is that some changes (resizing from any corner) are logical and sensible. Some changes (record screen in QuickTime) are practical and functional. Some changes (making everything in Finder a bland gray instead of colorful icons) make absolutely no sense. Some changes (Forcing users to either pay for or "hack" their own restore media) are outrageous.
Do you know what I measure my opinions by?
If Microsoft did the same thing, would they get hell for it? If Microsoft all of a sudden released an OS without cut and paste would they get hell for it? Absolutely. If Apple removed the "Copy Item" from the right click, the Jobsians would just say "oh, that's not a big deal, just drag it", because there are people swarming MacRumors who excuse every single pointless change. There's actually another post somewhere that I can't find at the moment where they said that if Jobs went blind and decided to remove the screen on every MacBook, the Jobsians would just say "we're post screen area, the future is touch only, sight unseen!"
I get that some of you don't understand the frustration but the frustration is valid. It's not just about Lion the system, it's about the entire ecosystem. Pointless changes, catering to an iOS crowd, STILL not fixing key things in the existing Mac OS (that you have to jump through hoops to do thumbnails on folders is laughable), charging for the ability to restore your computer if you don't have internet access, forcing hardware that is otherwise capable of running Snow Leopard to run Lion instead, and Jobsians who make excuses for all of the above. It's nauseating. It makes me wish I didn't like the Mac hardware in the first place. It actually makes me yearn for the day when Apple is led by someone who is the opposite of what Jobs is today and starts releasing the polar opposite of Jobs' vision. I eagerly anticipate all of the whining, crying and complaining about why their favorite computers have been relegated to actual work machines instead of "easy".