I dunno - it seems that A LOT of people prefer discussing matters of private importance on each other's walls, instead of each other's PMs. Most messages between people are in fact wall-messages instead of private messages. Why do you prefer that? Do you really want everyone to see your wall posts? I mean, if you were given the choice EXPLICITLY, wouldn't you say that you probably wouldn't want everyone to see them?
As for me though, I don't really care. I like posting my thoughts publicly.