Disclaimer: This is just, like, my opinion, man. Also, I won't be discussing whether MakerBot has done anything illegal or not; I'll only be explaining what I think is going on at the company.
Recently, the MakerBot Replicator 2 was announced as a closed-source device. This didn't really surprise me. In fact, I'm more surprised they didn't do this with the original Replicator. Yes, they're a company we've all come to know and love, but I've felt that for a while now that they've been becoming less and less relevant to the community of 3D printing tinkerers.
They Want to Change the World:
I feel that if MakerBot can make a very good 3D printer that requires almost no tuning or configuration for under $5000, they should go right ahead and do it—open source or not. I started 3D printing on a MakerBot, but that was with the Cupcake CNC, a completely experimental device. The end goal for me really wasn't to make little plastic objects; my goal was to build a really cool machine and to learn from the experience. I did learn a lot from the experience, but I don't think MakerBot is targeting people like me any more. I think they want to make a 3D printer that anyone can use, regardless of their tinkering ability. Is this a good thing? I think so! Why? Because it gets the technology into the hands of more people!
One of the biggest issues with the DIY 3D printer market now is that it is extremely price-sensitive. This is because there are many more choices for 3D printer kits available now than there were back when I was first starting out. I don't think it would even be possible for MakerBot to make a better product like they've done while still being able to compete because people looking for kits are looking to save money and/or tinker. Essentially, they've switched from making kits for tinkerers to making finished products for schools, small businesses, and individuals whose time is more valuable than money because the tinkerers no longer want MakerBot's products.
Open or Closed?:
Even though MakerBot has gone closed-source, I think it's for the best. Because they've made this amazing technology easier to use, they've been able to get it into the hands of more and more creative people. Making anything open source is never as simple as just "posting the files on the web somewhere." By not keeping it open source, MakerBot is able to focus more of its energy to improving the product because they no longer have to worry about documenting all their designs or supporting tinkerers. MakerBot, quite simply, no longer has any incentive to remain open source. Yes, they're pretty much becoming Apple, but I don't think that's a bad thing.
tl;dr: MakerBot would not be able to survive if it didn't change its target market and lose its open source nature in the process.
Detailed Economics Stuff:
The price elasticity of demand for 3D printer kits is a lot greater than 1 because there are so many equivalent substitutes. The opportunity cost for small businesses and schools to build and maintain their own 3D printers is a lot more than the price of a MakerBot Replicator 2 + support fees. MakerBot saw that there was a demand for an inexpensive, "zero-configuration" 3D printer for schools and SMBs and, seeing that the market they were currently competing in no longer desired enough of their products, they decided to switch markets to one that would pay more money for better quality.