I agree that a few bad postseasons doesn't mean he is a bad playoff goalie but that is certainly his weakness as of right now.
He just has a very unimpressive record. He has either been part of a meltdown or done fairly well when the team in front of him is doing well. There are really no instances of him stealing a series or being the reason the Habs have succeeded.
Look at all the other "top" goalies (I'm going to exclude Rinne because I think he is just overrated) - Lundqvist, Quick and Rask (IMO at least).
All three have taken their teams to the SCF and been a huge, if not the biggest, part of their team getting there. Lundqvist last season, Quick in 2012 and Rask in 2013 (especially the Pens series). Rask and Lundqvist also have fantastic regular season stats.
Until Price is part of a deep PO run, he will always have a knock against him. And maybe he will change that his season, who knows.