Mozilla and Opera have promised everyone that they would be sued for royalties (and there's no reason not to believe them), but I've never seen evidence of this. Nobody is ever going to sue Perian/ffdshow/VLC for royalties.
Still, even if they probably won't get sued they would always have it hanging over their heads. Making an investment in technologies which even have a small chance of causing legal trouble at some point in the future could be a bad bet for them.