Lakers gave up Peeler & Lynch for a draft pick to make room for Shaq. Also traded away Vlade for a 17-year old who could not really be counted on to contribute in year 1.
While Shaq is much better than Dwight, the effects of losing Peeler & Lynch were felt throughout the first season, and to an extent, the Lakers lacked the kind of scrappy players they needed until Phil came in and got some vets (AC Green, Jon Salley, Ron Harper) to do a lot of the necessary dirty work.
The Rockets will miss some things if they acquire Dwight. But, they can bring in talent to replace these guys. It almost always happens when these types of moves are made.
Miami traded away Odom, Butler, and Grant to get Shaq. They missed different things those guys brought to the table; however, because they had Shaq + Wade, it was easier for them to fill out the roster. Plus, role players have a tendency to improve when they are playing alongside more stars.
For Houston, this is absolutely the right move. For now, and for the next few years. But it isn't necessarily the best move for Dwight.