In the very first sentence of THG trilogy, Katniss wakes up alone in bed without Prim. At the end of the trilogy, she is again without Prim, but Peeta is now sharing a bed with her. This, perhaps more than anything else, is why I believe the "You love me, real or not real?" moment occurs in bed. In addition to the little hints, like "so after" or the fact that Peeta is there when Katniss awakes from nightmares, Katniss no longer being in bed alone would bring things full-circle quite nicely.
This just made my whole night, anon. What a perfectly subtle but beautiful way to bookend the series. Nice catch!