In the autumn of 1980, Bill's unfamiliarity with his new purchase [of QDOS] didn't stop him proposing, in a story told by Stanford's John Wharton who was Intel's second point man for negotiations, a three way carve up of the market between IBM, Intel and Microsoft - then a company with 30 employees. If historians are to conclude that Bill "thought big", they'll be correct - but they may also conclude that he didn't always "think legally". Market carve ups are a violation of antitrust laws.
http://www.theregister.co.uk/2006/06/17/saint_bill/
That said: Gates's comment that core programming teams are generally 4-5 devs suggests a pretty strong constant through the industry. It's rare for any specific module to grow much beyond that -- where you do see more people working on a particular piece of code, it's typically either highly modularized (and module contributors are working on sub-pieces), or the architecture is already highly refined, and the process is largely one of providing bugfixes or additional features to an established base.