actually, i think it might be more about generating revenue for facebook. I've received very little spam in my 'other' box, and a spam filter would probably be pretty effective at reducing that anyway (were it even an issue). I think the spam thing is just an excuse, so facebook can give you the option to pay $1 to get your message to the recipient's regular inbox.
But yeah, this is old news and I'm surprised anyone is just now learning about it.
But yeah, this is old news and I'm surprised anyone is just now learning about it.