That is true. The API's are high-level so the hardware implementation is not the most important. Still, it might create performance diferences since engines do use low-level programming that might need to be optimised differently.
Offering great dev tools is, no doubt, the most important step to get third-party support. But I think that the same architecture would also be a nice step in that direction. Especially since I'm a big supporter of console homogenization.
I'm actually really hoping they're going to provide better dev tools and documentation because that has been an issue. They need to get out of that of that odd habit.
I get the idea of console homogenization, but I think what Nintendo is going for is a universal platform all on the same architecture. Like all those Apple devices out there running on ARM. That could be their way to homogenize their own ecosystem. I dunno how things will exactly go on a bunch of this stuff but it certainly is interesting the direction Nintendo, and this industry is going right now.