10) He is an idiot.
9) He didn't want this page to be up on time.
8) He is an idiot.
7) He felt that "retarded" was politically incorrect.
6) His "R" key only had one more use left in it.
5) The Devil made him do it.
4) A potato bug crawled into his keyboard as he was typing and got
under the "R" key.
3) He did it to spite me.
3b) He wanted me to stay up late tonight, putting up the page all
by myself.
2) The misspelling was a metaphor for today's youth. In a way, we
are all misspelled.
and finally, the worst reason:
1) It was an accident (riiiight).