He is telling you, if you have the balls to hit the metal and the balls to work it out and the staying power to get something finished, working and great on that little machine then you have what it takes to go all the way.
I'm sorry, did he say that before or after mentioning that he had spent the week writing 3D code for Fountainhead? Because I must've missed it. :P
Seriously though, that doesn't make any sense: If you're going to apply the "not built here" mentality to DS development then you wouldn't be arguing for sanctioned homebrew solutions because, by that measure, the 'worthy' would be the ones that needed no help whatsoever.
I think you're right, mind, that being able to cope with all the low level stuff would increase your employability, but id write engines for people to license and I really doubt that he's trying to argue himself out of business.
[EDIT: Honestly, I just took his comments to be a bit of a lament, from a technologist, that not enough people in the field are like-minded and similarly skilled. If you write homebrew games you probably utilise some sort of API and will fit into a games company as a scripter/level designer I guess; the people who get employed to create the underlying technology write compilers for fun, not games. They're two different sets of people.]