Only, the fact that John McCain can't use a computer means exactly that: John McCain can't use a computer.
Not as in "doesn't know how," but as in "is physically unable."
According to a Boston Globe article from March, 2000:
McCain gets emotional at the mention of military families needing food stamps or veterans lacking health care. The outrage comes from inside: McCain's severe war injuries prevent him from combing his hair, typing on a keyboard, or tying his shoes. Friends marvel at McCain's encyclopedic knowledge of sports. He's an avid fan - Ted Williams is his hero - but he can't raise his arm above his shoulder to throw a baseball.
Obama had a "Biden moment."
Less than a week ago, Biden told Missouri State Senator Chuck Graham, to "Chuck, stand up, let the people see you." The thing is, Graham is a paraplegic, and can't stand up.
As in McCain can't use a computer.
And, to Obama, McCain's physically disability is ad fodder.
UPDATE: Scott Ott (ScrappleFace) makes the same point. But funny.