Speaking purely from my own perspective, I'd echo some of the perspectives above, Isfahan's especially. At it's core, I just think reading the misspellings verbatim is funny, because (in one way or another) it reflects the mind that wrote the piece. Be they ESL, in a hurry, inattentive, lazy, misspelling on purpose, has language gaps, or purely stupid, and I think the posts can be any combination of those.
I have friends who spell very poorly indeed, and I'm enough of a pedant that I always send text messages with accurate spelling and capitalization, so much so that I correct spelling or autocorrect mistakes when the intention is clear anyway. I never use U or 2 or whatever as word substitutes, primarily because I don't feel like it's a worthwhile sacrifice of clarity to type one or two less characters. But if I was reading the writing of my poor-spelling friends aloud, I would include their spelling mistakes - the message is slightly opaque because of these mistakes, but that doesn't carry the inferrence that my friends are dumb.
I think over the years, we've scaled back on our focus on making sure we nail each and every misspelling in what we read (for example, it's really incorrect of us to assert that "u" by itself would be pronounced "ooo"), but I still do love it when one reader will correct another for reading something correctly.