Seatguru says it's because at Row 41, the seats slight angled towards the outside, following the curvature of the fuselage, resulting in a tiny tiny bit extra legroom for the A and L seat. In my humble opinion, that increase is insignificant. Personally, I would not get a window seat on CO's 777 except for Row 16, 32 and 44. Way too hard to get out from any other window seat, and that makes me claustrophobic.