Have you ever heard of the term "universal design?" Look it up. We have students at our university majoring in computer science with severe multiple disabilities.
McCain certainly has no problem pushing buttons on a telephone since that is his motus operandi. If he can do that, certainly he could use a Blackberry for email since it uses the same fine motor skills as using a cell phone.
And don't blah blah about his disability getting in the way. Throughout my career in Special Education I've come across many kids and young adults who use assistive technology devices to help with computer and communication skills -- People with cerebral palsy who have absolutely no use of their arms and can't speak, but can communicate with computers and technology.
There are companies like ability hub
http://abilityhub.com/ who design mouse and keyboard alternatives. Or companies like abilitynet
http://www.abilitynet.org.uk/ who
help people with disabilities utilize computers and other forms of technology. There's also speech recognition programs that one can use and doesn't even have to touch a keyboard. However, many people with disabilities don't have the financial resources that McCain has to connect with the technology. Many programs to help people with disabilities are cut out of the budget by conservatives, but now you are trying to use this as an excuse?
He's just like your typical grandpa who doesn't need/want a computer. But McCain wants to be the leader of our country with any technology skills. Now that's scary!!!