There's a limit to the amount of developer time they can spend on any project; if the devs spend their time scanning forums and such, they're not spending it on improving the product.
That's why they set up UserVoice. It's a way of concentrating the voices of users into one easily accessible place. And instead of a lot of scattered messages, UserVoice allows us to vote for the features we most want and ignore the ones we don't care
about. The more votes, the more likely a feature is to get implemented.
Most important to understand: the iPad/iPhone etc versions of Office are still new and still VERY much works in progress. MS released them with the set of features that seemed most important and have been updating them steadily since, adding the features
that users most often ask for. UserVoice is a direct pipe to the "Users most often ask for" Big Pile o' Stuff for the Devs To Do Next pile at MS.
It'll take a few minutes max to cast your vote for a feature that's important to you. If nobody asks for it or votes for it, I wouldn't expect to see it soon.