I get the impression that it's one of the relatively small and relatively rare perks some staffers enjoy, so unless the guest is made uncomfortable or there's massive abuse I'd think it was natural.

Else that would mean that chronic staffers never get the chance to have things signed, no?

I do know that in a few (mainly media) conventions of the recent past there has been a feeling that (some) con runners have organized an event basically as an excuse to meet/socialize with their guests while having other people (attendees) foot the bill for them. But that's a whole other ball of wax.