Part of that comes from having a very small programming staff, originally just me until 3.0, and then just Keith and myself after 3.0. That makes it so there isn't a hodgepodge of styles and techniques and code branch merges going on, and that also makes it so that all the programming staff has a pretty full understanding of the architecture of the program, and how not to break it. One of the many advantages of a small professional team rather than a sprawling one (obviously small hobbyist teams without a lot of professional background in these sorts of programs run into all sorts of trouble even with just a programmer or two -- my earlier solo projects, all unreleased, are evidence enough of that!).