Considering the fact that ET is a free game and anyone can aquire a new GUID immediately, it's no wonder that since PBBans opened it's doors ET has accumulated 40000+ bans.
On the flip side of the coin, COD4 has only been out on the PC for 9 months and has already accumulated over 10000 bans... and as we all know COD4 is a pay for game. I think a large proportion of cheaters have found a new home with COD4 ;)