Howard could be, but he needs more offensive game. Durant will get there. Williams probably more than Paul.
For a lot of the other guys, look at what they'll be making at the end of their career. If Duncan got the max, would he still be worth 20 million a year at 39 or 40? Rose hasn't done nearly enough to be a max guy. Is he a very good player? Absolutely. And as much as I love Lee, someone will overpay for him. Just like the Sixers did with Andre Miller and Samuel Dalembert (don't think either was a max deal, but they were compensated too well for their talents). Dalembert especially was getting 2nd man money when he was the third best player.
These max deals are a lot like the HoF (which is a joke in basketball, but that's another topic entirely).
It's the Hall of Fame, not the Hall of Very Good to almost Great. A lot of these guys won't be worth the 20 million a year at the end (see: Shaquille O'Neal, Jermaine O'Neal, Tracy McGrady). And two of those guys probably weren't worth it to begin with.
To me, the max deals should be reserved for the elite. By definition, it shouldn't be that many of them.