Wade and Roy get votes into the next tier because of how they influence games on both sides of the ball. Wade a good bit less than he used to on defense, but they both can bring something solid in terms of team defense and leadership on that side of the ball. Health is an issue, but ain't that the case with every generation of tier 2 kinda votes
Guys like Allen, Iverson, and Carter are on the downside of incredible careers. Carter has done a good job or reinventing his game into one that doesn't need his atheletism as much, but he takes just as much time off on the defensive end as AI does. Allen will have game as long as he can shoot and not have knee problems - that is, within the next 2 years he'd probably be about done playing. AI can move, still. Question is if he can change his game to be a PG on the decline more than a SG on the decline. If so, he's got a good 5 years left (which is scary considering how much he has played already minutes wise).
McGrady should be counted as above, but something just says that he's more unrealized potential than anything else. I'm still of the camp that says he should have stayed with VC in Toronto and became that 1-2 punch of the 21st century.
Iggy is interesting here; he will probably end up as a bit of a Kobe-light in respect to all around effectiveness. He has all the tools, but hasn't exactly displayed that competitive side that just says that he won't be denied. Compared to everyone on the list not named Kobe, he will be known just as much for defense as he is for offense. But may end up reframing his game like VC on the offensive side so that he can stay in the L a few extra years.