I'm sure Microsoft is going to do the best they can.
That said, I wish people would realize that sometimes companies just can't make every major system software update retroactively compatible to every device ever made. It's not fair to expect that, and if they do focus on supporting people with 3 year old phones as a main priority, that could easily hold back progress and keep WP8 from being as good as it could be.
Personally, I think the onerous demands for endless backwards compatibility have held Windows desktop OS's from being as good as they could be for years. There's just so many people, companies etc, out there clinging to Windows XP and crappy old software and 7 year old PC's that Microsoft has to work twice as hard to escape the inertia.
So, yes, hopefully WP8 will be available for all the phones, but to expect that, to think you're entitled to demand it for a 3 year old phone or you're going to throw a temper tantrum and go to another OS I think it's a little ridiculous.
I will be delighted if we can all have Apollo, but barring that, a nice refresh update that takes care of a few of the major requested missing features and a taste of Apollo stuff would be a satisfactory concession prize IMO.
I'm not a developer, but I do understand Apollo is not like the upgrade from 7 to Mango. It's a major rewrite of the whole enchilada. Entirely new kernel, no more Win CE 6.0, based on the NT kernel instead like the desktop OS's. It's major stuff.