It's true as Nintendo decided to not use the standard x86 architecture, whereas Sony and Microsoft learnt this time around that using a standard architecture makes sense in the long run. 

He specifically said that this doesn't really apply to exclusives.

Developing only on a dev kit would blow out development time.
Game development needs workstation levels of performance, not anemic (Relatively) console levels of performance.

The point of a Dev kit is so that they can get the game running on the console hardware, they can debug, optimize, adjust everything so it can be the best it can be on that particular hardware set. And that also takes time to do.

Can you develop a game on a Dev-kit? Sure. But you can also develop a game on a phone or a tablet.
The caveat is that it will not allow you to be as productive as possible, especially when it comes to things like compiling.

For instance compiling a AAA game on a Phone would likely take you days, maybe even over a month.
On a Workstation with distributed compilers? Probably only talking a couple of hours.

You are right that there is no ".exe" of these games, but there also doesn't need to be one. They aren't games in a traditional package.

that seems rediculously vague, wouldnt it largely depend on the size & scope of the game?

Perhaps this may not be the case with all PC games. I imagine small size games wouldn't take a year to do

Eh, while Miyamoto knows a lot about game development at Nintendo, I frankly can't say I take his word on this
.

Maybe if this is a high end PC game where you have to adapt all possible control options but I can not think that you couldn't adapt a mid range PC title fairly quick.

you can port an existing game to any modern console in a year, much much less for ps4/xbo, too.

Hell you could probably port a modern pc game to Ps2 in that amount of time.

Miyamoto probably meant it'll take a year if you work with one hand and move 10x slower than normal. That seems much more legit than just a vague one year time span.

some of those games are made in one year - never mind port them.