The problem is dev time. Manufacturers have a road map for releasing phones to specific carriers. If an OS update comes down the pipe during development for the phone they have to make a determination on how long it will take to adapt it to their hardware, how long to test the new software and what the impact is to their roadmap. With the Droid X I'm pretty sure testing was done already so they had to launch with 2.1 and work on the update. With the Droid 2 they probably hadn't started testing the 2.1 build yet, so it made sense to launch with 2.2.
You also have to remember that Motorola and HTC aren't Cyanogen. There are very strict amounts of testing required because they have liability for malfunctioning software. There is a lot of time involved in testing a new ROM.