Obviously, YCombinator doesn't want its job board to turn into a free version of Dice. ...yet I suggest that it would be a big boon to the community of people interested in startups, at little or not cost to YC, to allow firms that have, say, less than 5 or 10 employees, to post to jobs.YC.
To give an example (and, yes, you caught me, this is a large percent of the reason that I brought the topic up) HeavyInk is looking to hire a Ruby / Rails rockstar to help us do something amazing in the comicbook space.