My memory is hazy so some of the details here might be a bit off, but the gist of this is correct:
Houston didn't get an NHL team because of a pissing match between Les Alexander (the former owner of the Rockets) and Chuck Watson (the owner of the Aeros, landlord for the old Rockets Arena, and the man who had the rights to a Houston hockey team). Alexander felt that Watson was overcharging him on rent at the Summit. Alexander also got the rights to the Toyota Center when it opened. To be petty he charged Watson exorbitant rent to play at Toyota Center. The Aeros moved to Des Moines because they refused to pay so much in rent, despite having the third(or so) highest attendance in the AHL. Alexander eventually sold the Rockets to Tillman Fertitta, who also has the rights to any NHL team in Houston, so things are at least smoothed out as far as ownership.
That being said the NHL has shown a tendency to place expansion teams in cities with no other sports teams rather than the major pro city/cities in their state (ie Columbus and Raleigh Durham). Still, the fact that Houston has an ownership group and arena already in place is a pretty big leg up, along with the population and wealth in the city. Fertitta bought the Rockets too late for Houston to be considered for expansion (and Seattle was a virtual lock anyway), but there has been a lot of talk about the Coyotes moving to Houston (Kansas City and Quebec are the two other names that come upmost frequently for relocation).