Do you have something else that relies on a specific version of Qt? I've tried this on a freshly-flashed device and it works fine, pulling in all dependencies without a problem.

I've seen one instance where it wouldn't install due to a bad dependency, and removing libqt* fixed it, but that also removed a whole bunch of other packages, so you might consider that a little heavy handed - perhaps removing just libqt4-maemo5* is sufficient (and allow the application manager to pull them in again when it installs Widgets Gallery).

I'd be interested to know what you find. Please let us know, and if there's something to correct, we'll do so.