Having been to the same show (Focus on Imaging) yesterday, I can say I was more than happy with Nikon letting me test the D7100, even with one of my own lenses (all be it for a warranty related query).
The Nikon reps had access to a whole array of bodies (D3200, D5200, D600, D7100, D4, D800 from what I remember), and also more lenses than I can possibly remember too. All you had to do was say, can I try this lens on this body, or can I now try this lens on a different body, or this body with this lens first and then that one after - and they would happily let you do that with little to no time limits on how long you 'played' with the equipment.
Most people treated the equipment with the care and common courtesy you'd expect, and having spoken to at least three different reps, the D7100s they had on display were not final manufacturing versions. One was actually on a beta firmware, another was a non RTM body, and they were also keen to point out, that the reasons they had these D7100s there was to ensure people got a good exposure to them as they were close to the final RTM versions.
They did the same last year when the D800 was introduced, and I remember from the hands on demos they allowed people then, that the reps had said, no one was allowed to use their own memory cards as any images were not being recorded on RTM versions of the camera, and because there was a possibility that people could potentially start placing review based on non-RTM kit, it would make Nikon look bad.
I'm guessing exactly the same reasoning is in use here for the D7100.
