I was thinking about this for a while and I realized a possible explanation.
The Droid X was updated first because of sales numbers. It's sold more units, so they wanted to update it first.
The Droid Pro, however, sold the least out of the three, but perhaps it's update passed testing sooner than the Droid 2 because there is only one version, whereas the Droid2 has two versions (Droid 2 and Droid 2 Global)
If, while testing the system updates, they find problems, they need to be fixed, then tested again, on both versions of the hardware.
This is just my speculation, who knows if it's true or not....
It's also a possibility that the Droid X and Droid Pro will get the update but ours won't. Of course that's a ridiculous and extremely lame possibility.