So if someone is a BTC holder and buys 10.000 LTC, intentionally, one block prior to the fork, and sells these 10.000 LTC back one block after the fork, then he'll suddenly have both his BTCs and the LTCs on the alternate fork.

Now, if and whenever some exchange adopts xLTC, then he'll have 10.000 LTC to spend / dump in the alternate fork. Yeah, I mean, what can possibly go wrong there... hmmm...