The WJC is a 19-year-old's tournament. For a 17-year-old's stock to drop, he has to play absolutely terrible in the tournament. Toews has not. He has not played as well as maybe some expected, after the way he played at camp and in the pre-tournament games, but I've seen many 17-year-olds struggle worse than him, and not have their status affected. (Most recent example would be Rick Nash).
Toews has been the best player at two tournaments against his own age group: the WU17, when he was the best player on the gold medal Team West, and the Junior World Cup, an under-18 tournament, which Canada won. That's why he's considered a consensus top five pick. The WU18 will be a big barometer. If he dominates the WU18 like he did the other two tournaments against those his own age, he'll be a lock for the top five, and the talk about him going No. 1 will really heat up.
Two players, IMO, have really improved their stock in this WJC: Erik Johnson, who is my top prospect for the draft, and Niklas Backstrom, who may have nudged his way into top five consideration.
The one player who has seen his stock drop is Jonessue (sp?) from Finland. He did nothing to impress me at the tournament, except for a couple PP chances against Canada, and may have fallen out of the top 10. (He's an 18-year-old, BTW). Frolik has not been as impressive at this year's WJC as last year, when scouts were talking about him as 1A behind Kessel, so his stock may have fallen, too.
The WJC is not the be-all and end-all for evaluating draft-eligible 17-year-olds. Anyone who knows anything about prospect evaluation will tell you that.