Licensing and support. Look at their other products; they aren't cheap. They are apparently coming out with a commercial version of Sencha Touch if you don't w

Licensing and support. Look at their other products; they aren't cheap. They are apparently coming out with a commercial version of Sencha Touch if you don't want to release your code as GPLv3. Like you said, it's javascript so it seems you could get away with using the open source version for commercial apps since the code is available anyway. But this was asked in their forum and the person was redirected to a licensing contact so they probably don't see it as so clear cut.