OK, so its more of an inside comedy thing. Like Gilbert Godfrey telling the plane crash joke at the Friar's Club roast shortly after 9/11 was "too soon" (go see "The Aristocrats").
I don't think the housing side of the punchline works as well with Wally -- he's too old. Asok's young enough to not yet own a house.
The primary one is that there isn't a punchline beyond just being a cheap pun. It's a joke based off of "Too Soon":
http://tvtropes.org/pmwiki/pmwiki.php/Main/TooSoon
It really is only funny because it is Asok saying it, and even then, it's only really funny as you could almost replace him with Wally for this strip.
Bitterly sweet and funny if you're not the one losing their home. OK, very funny. As to "Moose", the punch line is that it is very much too soon to have someone profit at a "next to nothing" discount as the bank hasn't even yet foreclosed. Maybe after a year or two the pain wouldn't be quite as acute.