So Monte Cook has walked out on D&D 5e... Cook has been responsible for a lot of D&D development over the past years; he first caught my eye with his Malhavoc imprint during 3e's halcyon years. When 4e was announced and I saw it wasn't to my liking, I certainly didn't blame him for creating that edition, nor do I blame him for 4e's abysmal track record.
When Wizards announced development was going to be wide open for D&D 5e, Penny Arcade pretty much summed up my own thoughts on the matter. Add to this all the varied "discussion" and edition warring I've witnessed on several sites and it's pretty obvious that while Wizards wants 5e to be embraced by everybody in the D&D sector of gaming, it's not going to be easy, if it's even possible. Cook stated his departure was over a difference of opinion between himself and the powers that be, not his fellow designers. In an additionally classy and professional move, he has declined to give further information.
Given the cynical and sarcastic nature of online gamer culture, Cook's move to not divulge anything further is truly refreshing. Still, closing the valve on the rumor engine's fuel tank hasn't stopped the speculation. A number of people on two specific sites (and no, I'm not going to link to them - you probably already know which ones they are ;) are already focusing their scattershot wit and intellect on whether Mr. Cook is being truthful with us, whether this foreshadows the doom of 5e, or whether Hasbro's bean counters are to blame.
My take on it is this: take the man's statements at face value, regardless of which edition(s) you favor. Monte evidently saw something he didn't like in the direction management wanted D&D to go in. As such, he stepped back from the project and left, citing professional differences and leaving it at that. Speculating on his motives - true or otherwise - isn't going to encourage him to divulge any juicy details, nor is it going to help close the rift generated by all the edition warring. Instead, it's like picking away a scab and then continuing to dig to find the source of the bleeding.
Sometimes it's better not to know. Sometimes a cigar is just a cigar. And sometimes it is better to just walk away and say nothing at all.