Probability theory dictates that certain events will have a tendency to cluster together. You'll find the same story with most products, some people having multiple dodgy Ford Focuses, multiple dodgy TVs, etc. Then you'll get the people who bought a product from a known bad batch, and it work perfectly for many years. Suffice it to say a thread dedicated to faulty 360's will rank up high in Google, so when someone has a problem they'll search Google for 'faulty Xbox', 'Xbox 360 red lights', etc. and come across that thread. Many will sign up on the forums and join in the 'discussion'. I've seen many threads in other forums praising the Xbox 360, are these just the anomolies?
Baring in mind 500,000 Xbox 360s were sold in Europe in December, if there are 2.5% faulty consoles, then that should mean 12,500 consoles are faulty in Europe alone. Similiar % fail in all electronic products, it just happens that the 360 community is very vocal right now. More than 500,000 will have been sold in Europe by now too, so the faulty number will be increasing. However, its still just 2-3%. You have a significantly higher chance of having an accident in your own home than getting a faulty Xbox 360.