At the time it was mentioned on the first page, DayZ (full loot, PvE, completely unrestricted PvP, permadeath) had 800K players in alpha. Now it's up to 1.3M players in alpha. At $30 to play, that's about $40M worth of popularity
I think in summary so far we can say that it's not possible to have popular game if it's full loot and open open pvp.
I think the distinction people are missing is comparing other kinds of MMOs to MMORPGs. DayZ is actually more of an MMO than most post WoW "MMORPG" games, but its far LESS of an RPG. In fact its not really at all.
No one in DayZ EXPECTS to live for ever, IE make it to level 80 in an MMORPG. And from my understanding there really isn't a leveling experience. I didn't really look into it too deeply.
There is really nothing a week or month old player in DayZ can't do that a 5 year player can do.
Losing everything is much more significant in an RPG game, even if its only gear and not 10% experience drops and what not.