As others have noted, there's a difference between offering data (which we do - we've spent a lot of time, money and effort to ensure that stuff like dumps.wikimedia.org works reliably even at enwiki scale) and providing a working environment for the dev community.
Having a primary working environment like Labs makes sense in much the same way that it makes sense to have a primary multimedia repository like Commons (and Wikidata, and in future probably a gadget repository, a Lua script repository, etc.). It enables community network effects and economies of scale that can't easily be replicated and reduces wasteful duplication of effort.
I'd like to go a little further on this point.
One of the goals of Labs is to have a fully virtualized clone of our entire infrastructure that is also completely puppetized in a way that's reusable by third parties. If you're worried about WMF, then you should participate in Labs. You should help puppetize and should help make everything usable by non-WMF entities.
Bringing community operations members back into the operations of the site is another one of the goals of Labs. If we have enough community operations people, then the projects aren't dependent on the knowledge of the staff to survive.
If WMF becomes evil, fork the entire infrastructure into EC2, Rackspace cloud, HP cloud, etc. and bring the community operations people along for the ride. Hell, use the replicated databases in Labs to populate your database in the cloud.
- Ryan