There's a massive inversion going on here. I'm saying that if Ogremoch has a power that causes earthquakes, PCs who fly to avoid it should indeed be able to avoid its effect, even if the crunch doesn't specifically say so. That is the exact opposite of screwing over the players.
There's a big difference between telling a player that the power he uses may not work in whatever situation rubs the DM the wrong way. Players may or may not know ahead of time why or when the DM will nerf their powers. As someone stated above it can lead players to simply pick damage only powers that have generic fluff lest they tempt fate.
Giving an NPC/Monster distinctive powers which help drive its story and make narrative sense OTOH is in no way shape or form impacting the players in a negative way, how could it? My monsters powers work almost entirely by the power of narrative. Monsters in general are narrative beasts with mechanics included purely to facilitate their use.
For that matter if you want to houserule PC powers AHEAD OF TIME before the player has to decide to take them and add many complex clauses explaining exactly when they're going to work and not work, that's at least consistent and I don't really see a downside except it probably clutters up the game with things that are really rather rarely significant.
Honestly, there's nothing wrong with weird situations interacting with powers. In general though I'd want to err on the side of letting the PCs have more cool results than taking things away. DMs seem always tempted to find reasons to nerf things. Instead add coolness by making things work BETTER sometimes. The warden's Earthquake power doesn't just make the earth move, it accesses the power of the elements. Even the very air shudders and tosses, water, fire, etc too. Not going to come up often, but it will neatly explain most anything and the player gets to think "Oh, cool, that's even better than I ever knew!" while in reality the game goes on ahead fine because he got exactly what the rules gave him anyway. Sometimes PCs will get more than they are entitled to even, but again that should be cool. Indeed Scorching Burst can set the grass huts on fire, yippee!
The end result is you can take the sharp lines drawn by the mechanics and just blend them in. I have never yet had to tell a player that something they could do didn't work in order to do this. Narrative is more flexible than most people seem to be wanting to give it credit for.