Allow me to enlighten you. "In development" is a very vague term. It doesn't necessarily mean that the game is being programmed or even worked on directly. They could have designed some of the Pokemon 7 years ago for previous games and decided that they didn't fit in too well (see the Munna in gen 1 theory), or been using previous games as a testing toy, such as the many eye-candy locations in B/W being a 3D object test. Development is weird. Heck, AlphaDream built the first DS with a burnt GBA, an SP, a link cable, and a Super Nintendo controller during "development"
Lies! I was never here! Purple taste like crayons.
I don't think any game has been in development for seven years. You know. Not counting MMOs that have been active for that long.
Duke Nukem: Forever Half Life 3
Duke Nukem: Forever was completely and unceremoniously abandoned. The recent release was probably made in a couple of years to cash in on the fanbase demand. As for Half Life 3, it may well be, or it may not have been. It may have been started from "scratch" (Fresh copy of the Source engine once again...) at some point.