If it (the " thing) does appear then I'd guess that it's an attempt to stop people getting up to mischief on the site. Generally attempts at hacking will involve inserting programming code where it shouldn't be and the quote symbol is used in code all the time.
The html equivalent of that symbol is " (with a semicolon at the end) and this renders any mischief as harmless gibberish if one is substituted for the other.
Maybe either that or to be compliant with web standards as they favour using html equivalents of things like the quotation mark and ampersand symbol etc.