But where this could come in handy is if you were not actually searching for an app, but then found out there WAS indeed "an app for that" in your regular search that you were not aware of.
Having to preface your search with "download" makes this kind of useless, though, from that perspective. If I wasn't thinking about downloading an app, I wouldn't be searching to download something in Safari since...you can't download stuff in Safari.
I tried this on my ipad, and it is not working.
Did you make sure to switch to Google Mobile? Maybe they didn't think to add the iPad as a recognized device for this feature (vs. iPhone, Android) because it's not considered a "mobile" device by default.