I feel all smug perusing The "Blog" of "Unnecessary" Quotation Marks. But really, why do I care? Maybe there's an answer here.
(via lowercase L)
An obsession with proper usage may be related to some kind of perfectionist streak, she says, or it could have to do with childhood patterns of wanting to please adults or teachers by doing things right. Putting somebody down by pointing out their bad spelling also could be a power thing.