I think he's grumpy because Wordpress's actions (and lack of actions) means the healthy marketplace for themes and plugins that could exist doesn't.
A lot of plugins and themes have been abandoned by their creators because they're walking away from unprofitable time sinks exactly as you suggest. The blogger is trying to point out Automattic is doing its users a disservice by keeping this environment.
I don't think he's approaching this from a user-centric perspective, but more from the perspective of how it's not "fair" to developers and designers. To wit:
Theme and plugin developers have helped make WordPress the champion blogging platform that it is today without receiving a single dime of the $29.5 million in funding that Automattic raised last year. Both Matt Mullenweg and his company Automattic benefit financially from the hard work of plugin developers and theme designers. Yet it’s somehow justified in Matt’s mind that it’s not okay for plugin developers and theme designers to directly receive financial compensation for their contributions to WordPress.
To me, that reads as "We've worked hard on Wordpress and we deserve to share in its success." The crazy thing is that a) as far as I can tell, not much has changed in terms of the rules, so if this wasn't a problem before, why is it a problem now? And, b) no one is saying that developers and designers can't offer premium themes and plugins for pay, just that Wordpress won't host those assets for them. How it that unreasonable? Again, this goes back to this guy thinking that he deserves to be able to charge for stuff that Wordpress is hosting for him, for free. Give me a break.
A lot of plugins and themes have been abandoned by their creators because they're walking away from unprofitable time sinks exactly as you suggest. The blogger is trying to point out Automattic is doing its users a disservice by keeping this environment.