In reply to mark k..

re: "...it requires them to be GPLed for no real reason."

Why do developers who want the freedom of distributing their code under a non-OSS license want to develop for the WP market for no real reason?

A WP marketplace that welcomes non-OSS based products would already have a reason not to get traction. The differentiating point with a Pro directory is that it makes it easy for people to find commercial plugins, which wp.org isn't for.