Just a few things I've noticed with the Droids multitouch implementation, what you'll need,
Simply Draw (multitouch drawing app)
MultiTouch Visualizer (self explanatory)
Smart Keyboard (multitouch keyboard)
Default Android Keyboard
First with simply draw, try and put both fingers very close together and draw, it misses the second touch until you space it apart. Bummer.
Now with multitouch visualizer, put one finger down and touch the other nearby, it only registers the second touch at a certain distance.
With Smart Keyboard, notice how the multitouch implementation works great across the board (test this by holding one key and pressing another), but with letters right next to each other, it drops the first touch.
Finally (and heres some proof that the default android keyboard is actually multitouch), do the same test as you did on smart keyboard. It doesn't visualize the second touch, but it does indeed register a second touch when holding a key. Until that is, you go to keys in close proximity, where it just thinks you slid your finger rather then pressed twice.
Now if this is the reason multitouch isn't fully utilized in the stock US version, I don't know. I don't even really miss it that much, its just a little surprising to me that other phones can do it relatively easily, but the droid struggles. I'd be curious to see how other android phones preformed in similar tests, maybe its something we can tweak or improve within the kernel