Fixed-lens digital cameras have several interesting advantages over interchangeable lens cameras. For starters, there's no particular constraint on the size of the sensor. Smaller sensors can use smaller lenses, and thus the whole package gets smaller and lighter. Furthermore, because the whole system is sealed, dust is just never an issue. And, on top of all that, when you're willing to go with an electronic viewfinder or a rangefinder system (i.e., get rid of the single-lens-reflex mirror and pentaprism), you can go with different styles of lens designs than allow the rear objective of the lens to be closer to the sensor (*).

All of that said, there are still fundamental advantages to interchangeable lenses. No all-in-one zoom lens can ever offer all of the qualities that can be found in more specialized (and expensive) lenses. And, for that reason alone, interchangeable lenses will be here to stay for a long time. An interesting question is what happens when the high-end integrated-lens cameras intersect in price with the low-end D-SLRs. I'll argue that D-SLRs win, not because they're necessarily any better at taking pictures, but because it's easier to sell somebody on future expandability (of which they may never take any advantage). Also, at least today, the D-SLRs just go faster, addressing probably the biggest complaint with other digital cameras.

(*) However, where film is pretty must just as sensitive to light coming in at an angle versus straight up-and-down, digital sensors are more particular about the angle of incidence. This is a real problem with the Epson R-D1 (basically, a Leica M-body compatible digital camera using the Sony 6MP sensor that's used in many D-SLRs). Because rangefinder lenses mount closer to the film plane, the angle of incidence at the corners is higher and, as a direct result, the R-D1 has problems with darker corners when using some wider-angle lenses.