I always wondered this too, if you sent the wrong amount I'm assuming (hoping) they'd still apply it to your account... since all bitcoin transactions are final and can't be 'undone' you'd be pretty screwed if they didn't apply it.
If this is the case, they should remove the amount in the dialog and just say "Please send your bitcoins to xxxxxxx"
AFAIK that's in the works for the new interface.