From my phone experiences, it isn't always a matter of a touch being shifted up/down by X everyone. Sometimes individual areas are screwed up. (as a simple experiment, I can put some water droplets on my nexus S and things go haywire unpredictably).

I'm doubtful this is malicious not so much because I'm some idealist that believes voter fraud doesn't happen, but because of all ways to commit fraud, this is a but ridiculous - it's obvious to everyone the machine is recording wrong and it will be noticed.