I'll add:
3) Horrific coaching.
4) Management made it clear they didn't want Iverson, he was just an expiring contract and they were looking past the 08-09 season. That certainly affected Iverson and also caused ...
5) Wallace and Hamilton mailing in at least major portions of the regular season and the entire postseason due to frustration with the team's direction. That had a lot more to do with Detroit's fall than Iverson's arrival.
6) Making young, overrated shooting guard Rodney Stuckey the team's point guard.
7) Tayshaun Prince being exposed as not that good.
For as much as credit as the story that Chauncey "turned around" Denver and Iverson hurt the Nuggets, consider this. The Nuggets won only four more games in 08-09 with Billups and Nene than they won in 07-08 with AI and Camby. And that was in a much weaker Western Conference (SA, NO, Utah, Phx, GS were substantially worse than the previous season, only Port was substantially better - the East was actually above .500 v the West last year).
That four game swing isn't a huge difference, the huge difference came in the fact that instead of being a 50-win 8 seed, as they were in 08, forced to start off against the Lakers who were absolutely rolling, they were a 54-win 2 seed, and got home court against the 7th seed Hornets who were the second or third worst team (ahead of Detroit and maybe Philly) in last year's playoffs and then the West's sixth seed Mavericks, who brain farted Game 3 or otherwise would've taken Denver to 7. Then they lose to the same Lakers team Iverson's Nuggets lost to the previous year (with a big difference being that the Lakers were tired from a 7 game series and struggling going into this year's series against Denver but fresh and rolling the year before). I just think the fall of Iverson and his "destruction" of Detroit was badly overplayed.