Quite a strange one here... Ico had zero freezes for me and ran perfectly but when it came to Shadow of the Colossus it appeared to crash at random when you were travelling across the world (jumping off the horse and walking for a while would stop it crashing). This 'compromise' worked for a while till the credits (yes, the last two Colossi had zero problems for me) where it froze. Yes, froze. The audio just looped for the last three seconds which was incredibly annoying.
Very tempted to sell this collection based on the frequency of these freezes!
Don't know if you care about this anymore, but Eurogamer wrote a Digital Foundry article on the Ico/SotC collection, and they mentioned that SotC was more taxing on the PS3 than Ico, and that encountered some performance issues running it at the default 1080p. Perhaps your PS3 is overheating or something? Just a possibility.