Did You Know WWW and Non-WWW are Two Different Sites?
If you're an SEO you certainly do lest you are malpracticing. And if you're a Cutlett, you've likely concurred here just a little while ago but more likely immediately.
Yet in spite of immediate pick-ups of everything Matt posts and that fact that this is a day later, Good God, I want to highlight his explanation of why, if only to be able to link to this portion of it when I am asked why and do a poor job explaining why:
Some people ask “Why don’t you just assume www.example.com and example.com are the same?� The answer is that they don’t have to be, and for some websites they are different. For example, http://phpicalendar.net/ is a different page than http://www.phpicalendar.net/. This happens more often than you might think; FindWhat has different www vs. non-www pages, for example.
Best and simplest it's ever been put.
Am I now a Cutlett, too?