When he talks about 200 themes were removed back in 2007 from the wordpress theme directory, most of the themes that were removed were sponsored(or spammy) themes. wordpress.org is is the website for the opensourced GPL'd project wordpress, there is no reason for them to host themes that run in contrary to that philosophy. The idea is to create trust in the hosted wordpress themes and plugins, for people who care they know if they go to wordpress.org, everything they download is GPL'd they are free to use, free to modify and free to redistribute.
I don't see that the onus is on Automattic to support any other agenda but their own, they are a business and the ultimate goal is to make money(for themselves).
That being said, the idea of a wordpress theme/plugin marketplace is a fine one, but as many people have already said in this thread it would be easy enough idea for automattic to take as their own. I would find it hard to believe the guys at automattic are stupid so if it doesn't exist already, there is probably a reason(ie/ profit margins are too low to spend the time developing the service, not enough demand, etc.)