Kahuna Burger, as it turns out, it is partially both. It's not that I have issues with the DM enforcing the rules on spotting an invisible creature, it's that I have a problem with the DM mandating that 1) Everyone can do it with great ease, and 2) Everyone is always attempting to do so.
So you were right. Perhaps it isn't a house rule, but it was an offhand post made by a slightly frustrated gamer. So, in order to put this thread back on track, a house rule that was odd to me is that the DM (and my other DM, who is friends with my first) has created a new skill called "Alertness". The house rule basically states that unless you're actively searching and alert for something to happen, you get a -10 penalty to all Spot and Listen checks. This can be helped by taking ranks in Alertness (modified by your wisdom), which is a class skill for everyone. For every rank you take, the -10 penalty is reduced by one. If you take ranks in it to the point where your total after wisdom modifier adjustment is above ten, you get a bonus to spot and listen for every point above ten on a one-for-one basis, but only when the character is "unaware".
This leads to characters who, when actively searching for something or listening, get a +6 or so modifer, but when staring at the wall and being thickheaded, the character gets a +11 or so.
Seems silly to me, really. Combine this with the whole invisibility issue I spoke of, and now it is more apparent why I've got so many issues with how the DM does things in this regard, seeing as how almost every NPC has very high ranks in the skill.