Gmail Spam Filters

Well, I have moved most of my email hosting over to Google Apps, but have found that a lot of spam gets through, albeit placed into my spam folder.

What I don't understand is how they seem to accept this even when they know it is spam. When will Google resolve its obsession with receiving and processing spam.

Its fairly easy to handle - just delete everything from the spam folder, but i was thinking that it shouldn't be there in the first place.