From my experiences living in Pa., where temps run from 90+ summers to 30 and lower winters, I will have to agree with you. My first house did not have AC and can attest to the dramatic sound changes with temperature that I experienced. A typical mid-summer day brought interior temps of 84-86 degrees in my listening room....add the heat from the old Krells and it would reach a shirt soaking 90 degrees. I'm sorry, but that will loosen up any flexible edge materials that I know of. As for the winter, temps would be right around 60-65 degrees causing materials to stiffen up.
The one pair of speakers that acted completely different from winter to summer in my house were the Thiel CS3.6's I had. I know exactly what you mean, as I can easily remember playing the soundtrack to "Glory" in which the opening track has some serious bass drum work and ends with a rumble and pipe chime. Winter time it sounded fine to me but summer time seemed to let the bass drum become much more visceral....to the point of feeling like there was a subwoofer added to the system. The same thing was evident with Pat Metheny's "Secret Stories" on track 3 about 3/4 through the track. Just after the orchestra swells to a fortissimo there is a nice set of pedal tones that underscore the ensueing melody of sustained notes by french horns. These pedal tones can only be heard from a FULL range speaker or a Sub. Again the same effect was felt in summer heat of a visceral impact and sustain of the pedal tones like a sub was added, where as winter just let the notes be heard but not really felt.