Rands speculates about the reason why WWDC is capped at 5,000 people and links it to the small team sizes at Apple.

When you talk about change or optimum team sizes, Dunbar’s number is usually thrown down as scientific evidence of something you already know in your bones. Shit gets weird somewhere between 100 and 200 people. You can no longer keep the individual state of each of the other people in your team or company in your head. Which means communication becomes more taxing. Rather than walking up to Fred and saying, “What’s up?” you cautiously walk up to a person you don’t know and sheepishly ask, “Yeah… who are you?”