- Centralizing copyright ownership in a single entity grants that entity the ability to lock down the project at any time and defeat the copyleft (e.g. Oracle killing off OpenSolaris). I consider this a worse outcome than a copyleft that is unenforced. It also encourages malicious enforcement (e.g. Oracle v. Google) that runs contrary to the goals of FOSS.
- Due to some very specific peculiarities of US law, regular users can sue companies that don't follow the GPL, because the source code disclosure requirement makes you a third-party beneficiary of the copyright license (which in US law is a contract).
The last one is a bit unfair to the article because the rulings in question happened after it was published. But it obviates the biggest benefit of centralized ownership - clear and unambiguous standing to sue. If things were the opposite - i.e. the courts said third-party beneficiaries can't sue and only owners can - then there would be an argument for keeping ownership of critical parts of the project in an entity with no conflict of interest against enforcement.
Even then, I don't see why ownership has to be centralized. Under US law, joint owners of a single copyrighted work both have standing to sue. Having more owners means more people with standing. In lieu of a classic CLA with a single point of failure, you could have a policy of accepting any code that is either owned by the developer itself (after their employment contracts have been vetted) or any of a number of trustworthy FOSS organizations who are committed to enforcing GPL. All parties would have standing to sue individually and could additionally sue as a class in a single action.