That was certainly my impression just from looking through the docs. Unfortunately there aren't many people doing cross-platform UI well, especially for games. The few decent open-source options (eg, CEGUI) don't support mobile at all.
This is a pain point for me too. I have an idea for a game, and since I love Python I'd love to write it in Python. But the available Python libraries for game UI all seem pretty dire.
(Outside games there's more general-purpose libraries like PyQT, wxPython, etc., but they feel more suited for general line-of-business type applications than games. And besides, trying to mix them together with something like pygame turns out to be a world of suck unto itself.)
I'd say kivy makes for a relatively good cross-platform UI for games. But for mobile games, kivy has the issue of producing very large download sizes, which may be a problem in selling it to a large audience.
