The HDMI route on old consoles is mostly for people who don't want an exclusive game monitor. They have a tv in their living room and want to be able to watch Blu-ray and play NES simply because it is the easier option. There are some who actually prefer the picture of HD NES, but it's the same type of people who stretch a 4:3 image to fit a 16:9 screen.
You could also ask why anyone would want to buy from the Wii Virtual Console. I played Super Mario Bros as a demo on the Wii U and died twice on the first level, even though I can easily get to 8-4 on the NES and SNES. It's very poor emulation, but the masses have bought the shit out of it.
Look at how many people are excited about the the NES mini thing. Why not just buy a modded Wii and play everything? It's still emulation, and the NES style controllers will be available all the same.