"We must assume that it's never too hot to dance."
And, whether that was Porter's commentary or, more probably by the Spewacks, I think it's also wry commentary on the changing language of musicals. I'm not going looking for the exact quote right now, but I know Porter had made apprehensive comments about writing the show, because he wasn't sure he could follow in R&H's footsteps in terms of changing the form. It seems to say to me that they all wanted a big dance number here, in terms of the show's arc, knowing full well that the reality of the scene worked against that. In earlier shows, this wouldn't have been so much of a problem, because dancing happened when the mood seemed to call for it. Now, dancing was only supposed to happen when the plot called for it. ;-)