[kqr]

I feel like that is due to physical constraints (are glass panes weaker at the corners?) than actual design-to-be-pleasing-to-look-at.

[canthonytucci]

It might also reduce the risk of (some kinds of) injury in an event where the people inside bounce around. Same for inside cars.

[IIsi50MHz]

Corners tend to focus force, so yes, glass corners are more at risk the further they are from round. There was an earlier airliner (whose name escapes me right now) which was noted for having squarer corners to its windows, and suffered more damage to glass and frames than rounder designs. I think it was retrofitted with rounder windows.