That makes sense, but then it begs the question of why Light Table was originally distributed under the GPL, i.e. since it's built from EPL'd software... and the GPL is incompatible with the EPL, as you say.
Does Light Table's new MIT license insulate developers from EPL-GPL compatibility concerns that might arise from the EPL'd pieces (Clojure/Script, et al.) used to build it?
A compiler or similar tool doesn't generally affect the license of its output (some of them explicitly disclaim that), just as a text editor doesn't affect the copyright of a novel written in it. The GPL is much more widely popular than the EPL, and now that it contains comparable patent language it is probably a better license to use (when the EPL was first written it was primarily to address patent issues that the GPLv2 didn't cover). I would hope that projects that are using the EPL would now migrate towards the GPL where possible - strong copyleft licenses are inherently impossible to combine, so it's best if the community can standardize on just one.
The MIT license is compatible with almost everything - it's really very minimal, comparable to a 2-clause BSD-style license. There is no problem combining MIT licensed components with EPL licensed components, or with GPLed components. (Of course there is still a problem if you want to combine with both at the same time)
http://opensource.org/licenses/EPL-1.0