Was seriously wondering that too? Why not 'toaster' or 'kettle' or just some other word(s) that could feesibly be associated with every day life/existance? Do they just say what they ideally want to, but somewhat inappropriately? i.e. "nice tits"!
I remember seeing something recently maybe on BBC3.... anyway there was a girl on it who said the word 'biscuits' hundreds and hundreds of times a day. She then commented something about not even particularly liking biscuits (this line was so wonderfully delivered) so I have no idea where they come from! I think the swearing one's just more publicised to be honest.
I find it really interesting that every person I've seen on TV etc with tourettes has got a cracking personality and usually seem to have quite the sense of humour about their condition.