Apple was awarded a "Multi Touch Input" patent. This patent covers using multi point contact on a computing device with a touch screen to implement input into that device. This INCLUDES pinch & zoom. The patent covers ALL multi-touch input in a touch screen computer device, not just pinch and zoom. (Here's an article on the patent
Apple Gets Their Multi-Touch Patent; Is Palm Screwed? )
Now, the reason Motorola/Google haven't implemented it on the base program is because they don't want to deal with the headache of fighting it if they can come up with options that work almost as well. Pick your battles. If a 3rd part app adds it, then let THEM fight with Apple but don't blatantly rip on their patent. All these other devices will probably run into trouble with Apple sooner or later. Apple just finished with Psystar so they now are free to pick their next fight. I personally don't miss pinch and zoom like I thought I would. What WOULD be cool is a press and drag option to highlight an area you want to zoom in on. I think that would be even better than pinch and zoom.