Shall there be no end to these threads?!? Yes, once you reach mid-level the game changes and it get's tougher on the DM (believe me, I know!). Yes, magic get's really powerful. Yes, a lot of things that use'd to be obstacles and threats to PCs cease to be a problem. There is no longer a need for jumping, climbing or swimming. Great distance is no longer a factor. Scavenging for food? That's for losers...
My question is:
lSo what?!?
Isn't it time by then to start introducing new obstacles and new threats? Shouldn't the game change as it progress? If you like everything to stay the way it is, stop giving out XP, leave the PCs at level 1 forever! If a 10th lvl fighter has no way of dealing with flying enemies, he needs to find himself a new game! One with no magic, no dragons, no technology and preferably no birds...
Remember that the PCs enemies probably also know of the existence of magic, and if they have a INT-score of more than 2 they will have taken some precaucions. The argument saying this is denying the PCs the use of their abilities just doesn't hold up. Having a defence against magic is an absolute must at mid/high levels and the evil guys should know this as well as the PCs. I don't hear any fighters complaining about his enemies having armors and shields, why should the spellcasters complain about magic defences? The higher the level of the game, the more important it gets. To an epic level fighter, his Mantle of Spellresistance is just as essential than his sword and armor...
I'm not denying the existence of 'broken' spells (Harm being an obvious example), I'm just saying that if a DM can't handle high-level magic users, the problem is not with the game...
Oops, I probably insulted a lot of people just know... Oh well, it had to be said! 