People are blaming Grubauer for the same reason that many are blaming Varlamov, because it is an easy and simple answer. It would be nice to think that goaltending is the primary issue, because it suggests an easier fix. While the goaltending has been spotty at times, the current issues with the Avs go far beyond who is playing in net. One issue is that the special teams have seemingly imploded. I don't know how big a part of the problem rests with the coaching, but it does seem like teams have really scouted and prepared for the Avs in all facets of play lately.
As far as Varlamov, I see that many posters are firmly behind him going forward, which is fine. I will say that it should be evident (or at least highly likely) that he will not be with the organization past July, if you can take Colorado's prior treatment of players approaching UFA status as any kind of precedent. Varly's latest injury woes likely only seal his fate with Colorado.