Nope, some people don't. They'll resurrect a thread without any real reason to do so.
On the critical annoyance meter, it's about a .1, and given the amount of traffic at TFL it's NOT that common occurrence.
Sometimes there are valid reasons for resurrecting an old thread. If all of the old threads were locked, though, that wouldn't be possible.
Frankly, we'd rather deal with the occasional misressurection than locking everything down.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.