I don't doubt for a second that the Purty has a lot do with Luci wanting Sam. (I wrote a whole fic about that being his ONLY reason) Who wouldn't want a smokin' bod while they off some Pagan gods? ;-)

But they keep making such an issue of Lucifer being able to take over the world once he's got said smokin' bod but not before. And now they're showing that he's perfectly capable of causing mass destruction of various powerful opponents even being all pock-marked and oogie. It just muddles the whole "Luci and Mike can't do their thing til Sam and Dean say 'Yes'" if they have Lucifer shown doing his thing. All very muddled and confusing to me...

But Purty... still very very Purty!