Jagex getting your IP is as simple as you logging into their website or the game. They see the connection from your address to their servers and then bam thats it, there is most likely a log of it kept. What they are saying is that they can't police individual addresses and find out if Sam DID actually get DDoSed or whether he just got real pissed one day and went PKing and died with all his most valuable shit. Its really important with all the DMM tourny hype and stuff similar to that.