I don't know if it's all spiders, but atleast one of them (Possibly just some common house-spider) has the mother give birth to hundreds of babies. The babies then hatch, and eventually the mother lets them eat her to death.
Sounds like a kick in the crotch after having to give birth to hundreds of spider eggs.
Also, I don't like spiders because apparantly I'm a mung.
They're just unusual and quite creepy when you find one next to you. Even if it's harmless, it's still not a necesarilly nice idea, that you've been sat next to one.
I should be used to spiders by now though, seeing as the last two houses I've lived in would get completely infested with them every winter and later in the hot summer.
I have yet to see a spider in my current house since we moved in, and that one was in the Bathroom. Because they just have to be there while you're sat down taking a crap. :/