I think your 2 points need a little more 'massaging'.
1) Avalanche snow can be porous. However, it can seal like concrete too, and does so the vast majority of time. (I use to live in Ft Collins, CO and my roommate of 2 years owned a trained Avalanche dog.) Friction from the falling snow heats it, thus, when it stops 'avalanching', it can 'solidify' into a very solid material - ice. (Note the use of the work 'can' ...) Yes, the point of snow on someone's roof isn't the same as an avalanche in that the roof's snow is free-layden (ie., not avalanching from the 'sky'.) BUT, as the heat rises up the attic space and through the ridge vent, it can melt the snow on the vent, and freeze it as the heated air is cooled whilst traveling THROUGH the porous snow (as you state.) I'd suspect that the heat rising up through the ridge vent isn't that great that it would melt the snow in short-order unless you're talking about a snow that's, well, maybe 1/4" thick. Of course, the sun might help this along but if the snow was a few inches thick, and the house was in the 'trees', then it would take a while for that snow to melt even with heat rising up through the ridge vent.
As to Point 2, check out the following:
... Statistically, half of completely buried avalanche victims suffocate within the first 20 minutes and less than 5 percent are alive after the first hour. Also, very few deep burials are recovered alive. In the U.S., since 1980, only two victims have been recovered alive from 6 foot burials and both of them were recovered extremely quickly by avalanche professionals.
Preliminary Report by Bruce Tremper and Carol Ciliberti Forest Service Utah Avalanche Forecast Center
The initial part of the statement states (I believe) that when a person breathes, it freezes the 'porous' snow, thus, suffocating them. (This goes to my point about the rising heat possibly freezing the snow at the ridge vent.) I think your statement of 'days later' is a reach when it comes to survivability (per the above write.) I guess if there was a real serious heat loss into the attic, and it was a sustained heat loss, the snow on the ridge vent would melt. I guess that if this is happening, folks would see their heating bill got through the roof too (not to coin a pun.)
Well, 'nough said. I just think your 1 and 2 aren't to be brushed aside as you insinuate.