They had some trouble scoring in the regular season this year, so I don't know that the premise of the thread is entirely relevant for this year's playoffs.
That said, no question their scoring has gone down in the playoffs the last couple of years, but at least consider that:
(1) scoring goes down for everyone in the playoffs (the weakest defensive teams tend to miss the playoffs), in part because...
(2) NHL officiating is moronic, and offers us the world's only sports league where the rules change for the tournament aspect of the season, almost in a conscious effort to render the regular season meaningless. "Let the players play" is just code for "let the teams who play a certain way do better than they ought to".
So I don't think the Canucks are alone in having their offensive players stifled a lot of the time. This is a common fan complaint about skilled players who are suddenly unable to play their game through no fault of their own. (Building a team "for the playoffs" from the get-go just leads to excruciatingly boring hockey, injured players and -- roughly half the time -- missing the playoffs anyway). The Sharks themselves didn't actually generate all that much last night, and I didn't particularly notice Thornton or Marleau.
But for the issues that are indeed team-specific, my own impression is that Vancityluongo is onto something that they seem to adjust the way they play in anticipation of (1) and (2) above. Which would be fine if it worked, but for the most part it doesn't, and to the extent that the Canucks have had some success (in 2011), I think a lot of that was in spite of changing their style. We all know the SJ series was different that year, and it appears to be largely because adapting to the Sharks' style of game led to Vancouver playing something much closer to what made it successful in the regular season.
Like everyone else here, I don't get why the Canucks always seem to mimic their opponent rather than vice versa, but I'm not convinced it's entirely coaching -- I think it is structurally easier in all sports to make a skilled team play boring than force a defensive team to open up. Destruction is easier than creation. (And coaches discovered this in 1993-94 when Anaheim and Florida were far better expansion teams than Ottawa and Tampa, and never really looked back).