DiPietro played better in his two post-draft junior seasons than Woo did. Then last season, DiPietro played at solidly 1A level as a rookie in the real AHL, which would translate to solid #3 defenceman (and that doesn't count the fact that goalies generally take an extra year to develop). For Woo to match that would require him to be playing at legit first-pair level this season in AHL Light with its watered-down calibre. I've only seen in him a Canuck scrimmage and the opening two AHL(L) games-- he didn't look out of place but certainly didn't strike me as a guy who was going to be a top-level player in that league this season. DiPietro seems to be a tier above Woo as a prospect.
Again, I don't want to sound like I'm down on Dipietro. I think he's a great prospect. As you say goalies take a little longer. I don't expect to see him in the NHL in a #2 role for a couple of more years at least.
My impressions of Woo have leaped quite a bit this year. Going into the year I would have said that he was a hit or miss prospect. He had some good attributes, particularly on the physical side, but were they translatable to the next level and would he have enough mobility to play well at the AHL level and project as a top 6 NHL D-man?
For me, the first answers to those questions came in the scrimmage games when he held his own against NHL calibre players. I thought, well some of the top end guys who didn't need to earn spots probably weren't going all that hard but at least he looked like he belonged. Then the first couple of games in Utica he held his own (but I wasn't watching that closely). What then took my interest to another level was his play with Rathbone. The two looked like a perfect match. He showed a lot of awareness of his partner's decisions, covered when necessary, was very solid defensively, and played physical. The two were arguably the top pairing on Utica when they played together. To me this bodes incredibly well for the future. Sure the AHL is watered down but it's still a whole lot better than the last level he played at and going into the season there were questions about how well he would make the transition. He's answered those questions in just a handful of games and now it would be surprising if he doesn't see at least some time on the NHL roster next season.