We do it for a pretty simple reason: Very rarely do two people actually have 100% the same problem.
WordPress is installed on myriad servers, with a variety of themes and plugins. The number of themes and plugins out there is a bit staggering, and when you've got 20,000+ possible plugins that two users may be using, it's not actually that often that it's 100% the same. Yes, sometimes it is, when everyone who uses a plugin has a problem, but then that's a plugin issue :)
In the case of that thread, we still have no idea if the original poster was using a plugin or not, so while it's likely they're related, we have 6 (you can't see the posts we deleted) people going 'Me to, but I was using a plugin...' and now that poor OP is going to get lost in the shuffle.
Which sucks for him, if he ever comes back at all. :(
And yes we deleted your other posts. We just like it if you make your own topics for problems, it helps us help you better :)
I would make a topic where you actually tell us what plugin you;re using. Maybe that plugin dev would like to know, so they could fix it?