Well I think that swelling only will occur when the moisture goes up. Also I think in newer homes the windows are more fire resistance and are a lot harder to break. But I do think that if it comes to that, than do it or do what ever you have to, to get out.

In what circumstances would the wood both be heated enough for that to make a difference and you'd still be able to escape in that direction?

I.e. if the wood is being heated by fire on either side....

Mine are significantly harder to open in the fall when temps are around 50F versus the summer when temps average 75F. Older windows are probably more prone than brand new ones.