[overgard]

> They almost never evolve their code bases to a second version.

This isn't necessarily true, a lot of code can and is reused between games (math, physics, audio, etc.)

In terms of isolation from the users, that isn't really true either -- the users are the rest of your team. You have to build tools for the team to use and they better be at least somewhat usable, and you need to have something workable quick so you're not blocking your artists and level designers, etc.