Actually, the original report is that what was announced in September was a far cry from what they originally wanted the watch to be during the early stages of development. Apple has reportedly spent years working on it, with the watch division sometimes being referred to as a "black hole" because it kept sucking down money. They couldn't get it all working properly due to issues with the sensors. Rather than keep delaying it, they went with something with sensors along the lines of a typical smartwatch.
Original report:
What Exactly Is an Apple Watch For? (
The Wall Street Journal)
Summary:
Apple tested (and cut) more advanced fitness sensors from the Apple Watch (
Ars Technica)
I've read some articles that misrepresent the information by saying things have changed drastically since the announcement, but that's not the case. The drastic changes came during the development phases.