I have heard this potential attack on transactions discussed. While this could be done what would likely happen is that other miners not being paid would pick up the "censored" transactions. This is one of many reasons keep mining dispersed through different jurisdictions. In general bitcoin's approach is based on incentives and if you want to do things like this it will be very expensive to do so and even if you can do them you can't do them for long.

Someone wrote a great article a while back that outlined many attack vectors that could be taken on bitcoin. I can't recall who wrote it or where.