Yup, this really pisses me off too.
I used to be a really serious grammar and punctuation Nazi but I had to stop because I fighting a losing battle.
It's purely down to the slang and abbreviations. People grow up saying "should've" so they don't know that it's "should have" and not "should of". Although if they knew anything about the English language they would punch themselves repeatedly in the face.
Our man Shakespeare would be spinning in his grave. I shall speak on his behalf.
Quoth the Bard:
"Share my lamentations, for thy language skills match not the scholar of yesteryear but the hick redneck yokul tramp of tomorrow"