The small subset applies to the set of startups that meet all the conditions noted. The suggestion is that 50/50 isn't a good idea unless your startup meets all the conditions. Most don't. But you might be right that most startups split equity evenly, even if according to the GP they shouldn't.
I created a poll, so maybe we can get some data: http://news.ycombinator.com/item?id=2445715