I'm pretty sure there is no grounds for "legal action" against Wube, should they ever lower the sale price of the game. You are obviously not a lawyer, and probably not familiar with European (or Czech) commercial law. (NB there are no "class action" lawsuits in Europe, and it's safe to say that no ...

I understand the position you're taking with this, but the yearly sales on Steam are typically great ways to advertise. Even a "sale" of like 5% off would allow you to get on the list of games on the front page, which is extra visibility.

Of course, if you don't actually need the extra visibility ...