Based on whats on the website:
P7100: Approx. 116.3 x 76.9 x 48.0 mm (4.6 x 3.1 x 1.9 in.), 395 grams inclu. batt & card.
P7700: Approx. 118.5 x 72.5 x 50.4 mm (4.7 x 2.9 x 2.0 in.), 392 grams inclu. batt & card.
Looks like the P7700 is slightly smaller in size compared to the P7100.
One of the better upgrades i would say is the swivel lcd screen which Canon has dropped from the G15.
Er... I don't think the P7700 is smaller. Infact it is abit wider and thicker when compared to P7100. But in my opinion, it look very good as compared to Canon's G15.