Pondering a moment from history.
1. One of things that I really didn't like about basic 1e was that apart from the wizards most of the PC's were almost entirely differentiated by the magic items which they had. This was one of the issues which drove us to Runequest, incidentally. In the stories we read it was the heroes characteristics which were most important, while in the game their characteristics and abilities were dwarfed in significance by the presence or absence of their magic items. Wizards (and to a lesser extent the other casting classes) had a lot more options and variety available to them, not to mention increased raw power.
2. One of the things that I really, really like about 3e is the way that the non-spell using classes now gain in capability more, and have a much wider range of directions which they can develop in, reducing the cookie-cutter effect. Any five fighters could be vastly different now. This has been a big help.
3. Personally, I think that some of the benefits of this have been offset by the surge in buffing magic and magic items. The bottomless (topless?) cap on spell Save DCs and AC means that the game is now designed around high level play where, in most cases, it is vital that the high level non-spell casters have a wide range of magical equipment... not just for differentiation but for survival!
4. Part of me wonders what 3e would have looked like if it had been designed in a way which didn't tie in "expected magic items" with level - or if the reasoning behind the tie was explicit rather than implicit. I imagine that it may have been a little like CR evaluation - guessing, followed by playtesting and eventually fitting into a formula which described the relationships (rather than being a straight derivation). I guess it probably wouldn't have been possible.
Cheers