Can someone give me a really good explanation as to why Research in Motion has yet to come out with a BlackBerry with a built-in digital camera?

When I started this blog almost two years ago, one of the top requests that many BlackBerry users around the world had was to add a digital camera to a BlackBerry that allows you to send pictures as attatchments. Nearly two years later this is still one of the biggest requests and I have no idea why RIM is so reluctant to go down this road.