Blizzard wanted "Warcraft in Space". Designers came up with gameplay, which would be hard to implement in the existing warcraft engine. Engineering told the designers; we can do everything you want, but then we need extra time to build a new engine first. Everyone agreed and the best game of all time was made.

The 'refactor' was integral to the success of starcraft, and is definitely a tradeoff that needs to be weighed for new products.