Not to mention how well they were playing at the end of last season. In the playoffs they played the Spurs better than anyone.
I'm not saying that I think Dallas is going to finish in the top 2-3 seeds in the West. However, if they're healthy, then I could easily see them getting hot and making a run in the playoffs. I certainly wouldn't want my team playing them early in the playoffs.
Hell, even with a healthy Harden and Dwight I still have Dallas being better than Houston and Memphis isn't out of the question either. Calling 2k flawed for Houston not being in the Top 10 in the Power Rankings (especially without context) is a little suspect.