Perhaps there is some insight in the 1UP.com review:

Seeing StarCraft: Ghost at all of its major surfacings over the past year and a half has been interesting. The game has looked pretty cool each time, but it's also looked different each time, suggesting that Blizzard is continually reworking what it wants to do with the game's level design and controls.

Some might take that as a bad sign, but it depends on your perspective. I'd rather see them keep working to create something they're happy with than simply steamroll ahead and release a game with a design that isn't the best they can do.

[ StarCraft: Ghost ]

And I think I have to agree, waiting an extra year to year and a half for a game is fine, if you know that it is improving the game by a year to a year and a half, and the delay isn't for other, stupider reasons...