Dunno about channel 5 my man, but I do know that the advert has been on Sky One - it shook me for six as well. I can only imagine that the networks have subsidised it or somrthing and have replay rights a coupla years from now.
Channel 4 have been quite aggressive in their advertising for a while now, taking out lots of press and billboard ads and paying for advertising time on other channels. It's nothing to do with replay rights or anything like that, it's simply Channel 4 buying time like any other advertiser.