Sorry but they really aren't. I don't know why people keep saying this. Assuming this whole 2 SKUs with a unified library thing is true then that would mean that all games would have to be created with assets that are at least acceptable on the stronger SKU, but also work on the weaker SKU, generally resources needed per game would rise and while there might be somewhat less long droughts Nintendo would surely not be able to adequately support the system on their own.
They dont need "differnt" assets.... they just need to bump up resolution and AA.
Watch this video: (same assets, same game, differnce is just resolution they are rendered at)
Psp resolution (480x272) vs PPSSPP (1280x720):