This is an issue i noticed when i used the new forge mode in halo reach, where you can edit the co-ordinates for a piece. the same graphical 'glitch' happens in Fallout.

Say the map designers have two pieces of wall they need to merge together, and they want it to look like one wall. they can probably edit where in the world it is, using a coordinate editor. they set the same coordinate for a specific axis, and its flush with the other wall

However, whenever youre ingame looking at it, and you move your camera, the game cant figure out which wall to show, since theyre in the exact same spot. the textures will flash and switch rapidly between the two walls.

It happens with walls, floors, buildings, and even mountains off in the distance.

This is called Z-Fighting and it's incredibly irritating. There's not really a good way to fix it, besides making sure the geometry ends, or moving one a miniscule bit further out from the other... but then you get a seam which can show under certain circumstances.

ah, good to know there was a name for it.

Seems a tad simple to fix, depending on how small the geometry can be, just set one wall the smallest distance behind the other. im not sure a ton of people would have a problem with that =D

Z-Fighting is the sort of thing I'd expect from a MOD; not a fully-priced game.

I don't mind glitches in-game, like Z-Fighting-, so long as they're not detrimental to the game-play and don't ruin my experience, but when it's an often occurrence it's quite irritating.

I can't quite see how it's so difficult to get walls aligned correctly. I spent a few hours trying to make a Left 4 Dead 2 map once using the Source SDK, and despite my inexperience and lack of a tutorial to follow, I still managed to avoid Z-Fighting errors. Surely a paid group of "professional" developers could do the same (not a direct dig at OE; most if not all game developers seem to do it).

While I agree with you, I should state I have seen this in a lot of games for the past couple years...

Fallout 3 Did do what the OP suggests, however this causes problems when viewing the surface from a nearby oblique angle. Paint and other decals seem to 'stand out' and parallax can be observed between then and the surface they are (supposed to be) on.

It's a tradeoff. If you don't put enough distance, you still get the fighting.

The real solution is at the engine level - decals should be painted into the texture PRIOR to rendering, rather than mid-pipeline as they are now. This is both harder to implement properly and more expensive, however.