Gotta agree with you Felon, Darkvision is a natural ability. Its even listed in the DMG as an extraordinary ability, which means it is not cancelled by a dispel magic, for example.
I'd say Darkvision works a lot like infa-red goggles work in real life- it registers heat differences between different types of materials, giving the viewer a rough idea of what is around him. However, extremely detailed analysis of objects simply wouldn't be possible. Although the detail that darkvision works in the presence of light is a little wonky, not to mention it would be extremely disorienting for a viewer holding a torch to percieve color and detail to a distance of 30 feet, then b/w past that for another 30 feet. Although I suppose that if you said beings with darkvision had rods/cones in their eyes that were sensitive to infa-red radiation that the brain interpreted as b/w images, it might make more sense.
I guess that leads into may bad house rule #1 that I have run into so many times in D&D: DMs who blissfully ignore real world physics, chemistry, and biology- in reply saying "its magic". Granted, some things are due to magic, but not everything (especially exceptional abilities).
Other annoying house rules I have run into:
#2- DMs who cater to their girlfriend by upping the power of whatever class, weapon, spells, etc their significant other is using.
#3- Magic item shops where PCs can walk in and find virtually anything available to buy (or worse yet, ordered from another outlet within the week!!!) Yes, I am talking about a franchised magic item shop. "Magitron Shack" anyone?
#4- DMs who don't understand alignment and say "You're CG, you CAN'T do that- its against your alignment!" Alignment is determined by actions, not actions by alignment.
#5- One of the worst- if an NPC is making a dramatic soliloqy, if a player interrupts to ask a question, the player's PC is docked 1000 XP!!! Yeah, that DM was a real drama queen.
However, I'd have to say that most house rules I have seen in practice haven't been bad. They are simply an attempt by the DM to make the rules fit to his setting- and nothing is wrong with that. I may not have agreed with some of them, but I understood what the DM was going for- and as long as the rest of the group was cool with it, I'd learn to adapt. I have to say though, there have been some real stinkers in this thread so far!