Just to try to clear some things up:

If you have the choice of developing a plugin and giving it away and putting it in a commercial repository who, in their right minds, would do the former?

They are not talking about offering a commercial "repository" ...just links to people that offer commercial support for their theme (and hopefully plugins eventually). I'd still give my plugins away because that lets them be in the wordpress.org repository (allowing for one click updates, update notices, etc). People selling their plugins cannot have them in the WordPress.org repository whether they're GPL or not, because Matt has stated that he does not foresee there being any method to sell plugins or themes on WordPress.org in the future.

The commercial theme repository was (I assume) created as the WordPress theme industry was deemed to be unacceptably biased towards non-GPL themes. However this does not seem to be the case with plugins. I don’t know of any popular non-GPL plugins but until recently I could rattle off the names of a whole stack of non-GPL themes, most of which were far better than their GPL counterparts.

So no, I don’t see much point in a commercial GPL plugin repository.

Again, this isn't another repository. However, putting that slight difference aside, there are plenty of plugin developers that are wanting to start charging for support. I myself am one of them, and so it Joost (http://yoast.com/on-the-gpl-themes-plugins-free/). Joost has popular plugins like Sociable, Breadcrumbs, and Google Analytics for WordPress. I have things like Twitter Widget Pro. Neither of us wants to charge for our plugins, but we want to charge for support. The problem is that once a plugin gets popular, you start to get TONS of requests to work on it. People actually think they are entitled to have you fix a glitch or add a feature. The problem is, that takes a lot of time and nets you $0. If I were to fix every issue and add every feature that came as a request, my family would starve because I couldn't do anything else. If I can charge something for support, I can better justify spending more time on them. I actually have plugins that I don't want to release because I know that as soon as I do I'll be getting a flood of support demands.

Now, having said all that, I can do all that with the current plugins repository and without a commercial plugins page. However, it seems to me that plugin developers who offer commercial support for their plugins should get the same treatment as theme designers that offer commercial support for their themes.

You can read more detail on my position at http://wpinformer.com/gpl-themes-love-plugins-suffer/