Time is a factor to consider for developers that spend most of their time developing, that is a valid argument. But depending on the scale of the game, I don't see there being much of difference. I'll return to this after I have tested it out, and let you know of my results.
It seems that only a select few people have actually tested it themselves, so this isn't a completely reliable place to go to for information. I think if anyone is going to think of trying it, they should just go for it, and learn from their mistakes if any are made. Supporting a platform as big as the Wii U will make you a lot more money than supporting mobile app stores. It's disappointing that we have yet to see much support from other platforms, but I wouldn't be surprised if that support is coming in the future. (Hopefully for C3).
Two reasons why I'd say to try it: Less games than other markets means less competition; and it's also a system specifically designed for gaming. A console. Besides from the fact of it's popularity going back up because of the fact that few newer games on the powerhouse/expensive consoles are good. (Though there are some very obvious exceptions to this... The Witcher 3...)