Why wouldn't KenzerCo "get away with it"?
People have been heavily propagandized when it comes to copyrights, trademarks, licenses, etc., over the last few years. Many think that our rights in those matters are less than what they really are. When they hear of someone making stuff like Kenzer is doing with Kalamar or the 4e Folio from Green Ronin, they envision swarms of lawyers making sure such people don't "get away with it."
The idea that one doesn't have to accept WotC's terms in the GSL is shocking to some.
Statements like Mr. Pramas' earlier in this thread can often be too much for those with such a simplistic view of copyright law:
"Game mechanics cannot be copyrighted, so people could take 4E ideas and bring them into 3E is they wanted. They just need to careful to rewrite everything because specific expression is protected by copyright."
And it goes further than that. You can take 4E ideas and use them in any system, under any license you have access to (including your rights under copyright law). There's nothing stopping someone, for example, from taking a 4E concept, making an original expression of it and releasing it under the OGL, Creative Commons, GPL, etc.,. As we speak, people are working on exactly such a project to OGLify 4E's core rules.
I'm a fan of GR's stuff. But I'm also a 4E fan. I'm definitely going to check out the Folio and any other 4E stuff they produce. True 20 is also very cool.