Joe, excellent question (and if you were the "Joe" for the DDI interview, that was a great feature)...
It was pretty clear to me that WotC hired Mike Mearls after "Iron Heroes" for 4th Edition (I flatly stated to a d20 writer friend that "they hired him for 4th edition work"). Mearls is a beast as far as volume of work and quality. Reading the preview for "Races & Classes", I got the sense that Mearls was heavily involved in the design process and was more of the "hitman" whereas the main dude was more like a "mob boss" (involved in the brain storming but not as much in the execution). This is ALL speculation on my part (which gets me in trouble).
Morbidly, WotC probably ramped up their hiring and staff for the creation and launch of 4E, and since we know what goes up must come down, there will likely be layoffs after the launch. I DO think that WotC may have a SMASHING hit on their hands with 4E, so maybe they will wait to see how sales go before deciding on layoffs.
In general, for me the designers/writers that get me juiced up most as a reader are those who have the rare combination of strong mechanical instincts (I guess this is the "designer") with very strong writing where you can TOTALLY SENSE (visual, tactile, etc) the flavor text that they are conveying. Long-time D&D players will likely want to play around with lots of mechanics, but mechanics are pretty lifeless and don't really inspire folks to buy books by themselves (?).
I don't truly know the strengths/weaknesses of those involved with design/writing 4E. My guess is that those who are the best WRITERS will likely have the most success and they will need the "numbers guys" (designers) to make sure the mechanics don't suck.