If it doesn't have a mirror, then it's not an SLR camera. It cannot be considered a digital SLR regardless of whether or not the lens is removable.

If it's not an SLR, then it's not - by ANY means - the first interchangeable lens digital camera. EPix launched their system using C-mount lenses in 1996, a digital still camera that was not only one of the first true digital cameras as we know them now (rather than the earliest ones which were digital video still caputure devices, or "Field Capture" - technology also integrated into some LaserDisc players of the era), but was also one of the real pioneers of integrated snap-shot digital photography in an era when scanning cameras were about the most useful tech around.

This isn't news - however, I don't recall reading about the Nikon D90, which HAS brought something new to the market, here.

How's that digital photography reporting going, eh?