Does seem like a bit of a hole that there's no United employee if you have some complicated check-in issue, or a re-routing issue that would make you already be physically at the airport but not want to clear security for whatever reason (e.g. your once-a-day int'l flight is cancelled, you don't like your auto-reroute, and you'd like to discuss your options before leaving the airport).

It would be cool (and probably against TSA procedure) to have a two-way facing Customer Service desk that could be approached landside or airside.