Voadam: While I do my best to avoid using them, its true that the DM has a large trove of these magical items and conveinant spell-like abilities that he sometimes turns to as well. No matter how much we'd like to pick on the PC's, I think we've all used Sertan's Substantial Sustenance Support to keep obviously broken ecologies running in our campaigns from time to time. Like, "Yes, it is a desert filled with nothing but large PC eating carnivores." and the classic, "Yes, it is a forest of mushrooms in a dry chamber that is never exposed to the sun and is not continually replenished by organic matter from the surface...but but... they are MAGIC mushrooms."
I try hard but... *shrug*
And how about Teller's Istananeous Town Guard Fortification for those times that the PC's start rolling the locals undesirably (or the plot requires the PC's to fear the town guard), and suddenly the town gaurd transforms from Warrior 2's to well equiped Fighter 4's with spell caster back up.
How about those Magnificent Instaneous Dungeons of Doom when we want to create some complex dungeon environment but we don't really want to dwell on the details of why this intricate complex was made other than to bewilder PC's.
I really try hard, but sometimes its just easier to brush the details under the rug and trust to the fact that the PC's will probably never have a big enough picture to realize (as you do) that the appearances of realism are only superficial.
And how about NPC Adventures Selective Amnesia Syndrome, that allows really nice treasures to be kept by mere Kobolds in dungeons rumored to contain treasure EVEN THOUGH there are NPC's roaming about of the same or higher level as the PC's who'd have no moral compunction about killing Kobolds and make a living doing what the PC's do. I mean sometimes its just darn conveinent to assume that the PC's are always getting there first.
I try. I really do. Most of my PC's never know that I use these DM powers from time to time. In fact, most are impressed by how my campaign 'realisticly' seems not to rely on such shananegon's.... but sometimes... the temptation is just too great, and though they may never catch me at it... I know.
Whatcha supposed to do? Realism or fun? Thought so.