Just because you are deaf doesn't mean you can go around messing up your typing.
Not being able to hear doesn't affect your typing.
Yes it does. Sign language is nothing like English. They may interpret the signs as English words but as most people fail to realise the grammar and sentence structure is dramatically different. "I washed my car last week" becomes "My car, I wash week-past" in sign language. Since he is deaf he uses sign language a lot in a day. Just like we use English, spoken or written. In other words American Sign Language is easier for him than written English. If he was born deaf then he has even less idea on how grammar in written English works.
If you seriously have problems reading his posts I suggest you brush up your language skills. I don't know any sign language grammar yet I can read his posts just fine.