The reason that I think the Pistons can be dismissed (and by dismissed I mean they will not win the title next year) is that their success was so dependent upon their starting 5. For the last few years, it has been the hands down best starting 5 in the league, and one of the very best defenses.
Their offense, which improved this season under Saunders, should be about the same if not improved. Their defense will be significantly less potent, though. Rasheed is not the shotblocker the team needs, and it is unlikely that they can acquire such a player. Also, the Pistons struggled at times with rebounding, and Ben's departure should only make that struggle more prominent.