Ideas can be copyrighted.

Also, yes, you can take him to court and win, if you can prove your case. Often times, all you need is a threat. Other times you need to actually file for the case and then settle before it goes.

He is right who carries the biggest stick. In this example, whatever company that made Tetris could most likely sue and win if a game came out that looked and behaved similar. For example, same or similar shapes with better graphics. There's many games that are very similar to tetris but they don't "cross the line". If you have the money and time and are confident you or your lawyer can persuade a judge that it was stolen intellectual property, then YOU will likely end up right.

Disclaimer: my answer is based on working in a law firm and having a friend that works in the intellectual copyright law arena, but in actuality this is pure opinion and I don't know anything at all.

EDIT: Also, I think you take pretty much anything to small claims court ("SUE EVERYBODY!"). AND the interesting thing here is that the person you sue is required to show up in YOUR court and if he doesn't show is almost always judged against. If he lives a few states away, this alone might be enough to persuade him, or the company, to "settle". Then again, I believe if he wins the actual case, calls your bluff so to speak, he can get you to pay court costs, including I believe his expenses (at least court costs for sure). So it pays, if I am right about this, to be sure you can prove your case.