The number of failures like this are pretty low, I've had a dozen or more Canon DSLR's with no issue, and I have friends with many more that have never had it.
That is no consolation for a owner that gets the problem. Switches are by nature unreliable, they can create their own failures and oxidation, no need for external debris. However, switch technology has greatly improved over the past years, computer keyboards are a example. They used to have switch failures frequently, but now they are improved, even though the price has been driven way down. They just learned how to make them better.
I have had both a 30D and a 40D develop shutter issues. The 30D did it after a couple months, the 40D had about 35K actuations when its problems developed. Of course, this is all anecdotal, but my experience with XXD shutter buttons has been less than stellar, FWIW.