He's too much of a professional to say so, but I think many people will get the feeling that this decison was motivated by "The AOL Way".
Dan Benjamin recorded a 40-minute interview with Josh three months ago. He talked about his experience becoming Engadget's editor-in-chief, coming from a background as a music producer:
I'll miss Josh's writing for one. Always enjoyed his articles even if I didn't always agree with him. Hope he surfaces again soon. Keep writing, Josh!
And AOL loses another editor. He says he'll be sticking around as editor-at-large, and co-hosting the podcast, so... maybe this is a way for him to keep writing without being under AOL's posting mandates?