Henry
Autoexreginated
I suppose it depends on what one means by "the system". I focus on the basic d20 mechanic, along with classes (having classes, not necessarily a specific set of classes), AC, the three saves (and how they work), and other generic features.
If that were the criteria, Basic Mentzer D&D would meet three of your four, the main difference being how saves are reached. Heck, there would be more of a difference between Original D&D and Mentzer Basic, because in original there were no saves! (That I recall -- I think it was added in one of those supplement books, because I don't remember a save chart in Men, Monsters, and Magic.)
I just have to disagree on whether it matters, though, because the OGL says it doesn't - it's meant to foster incremental improvements as well as broad-stroke improvements. In fact, Paizo could one day prove Ryan Dancey a prophet in an old article where he talks about people picking up an OGL D&D if the owner of D&D makes changes too unpopular with the gamer majority.

I see where you're coming from though -- I'm guessing you see it as too close broad-mechanical-strokes-wise to be a different system. I'm seeing it as almost as different as 4E is from 3E. Would you say 4E is a different system from 3E, at least?