Your point dosn't make sense from a consumer-standpoint. :-/
Every extra option you have to upgrade both speed and size of your storage, clearly it is a good thing - it dosn't matter if you are a core gamer or not.
It's the same as having Dead Rising 3 on Xbox One - compared to Call of Duty or Fifa - it's a niche franchise wich only core gamers know about. :-/
However - Xbox One's game portofolio is clearly much better with the ability to play a zombie-game aswell as the much more important CoD and Fifa.
The Wii U also offer you options - it dosn't have much of original storage - but it got lot's of great external storage options from third parties - but a console usually located in the living room, and if I were to guess - I would guess the concept of putting extra boxes in your living room is also pretty offputting to many consumers - but with more options to improve your game-experience - you still have a option to improve your gaming experience, and with many different boxes to put beside the Wii U, it dosn't hit you so hard in the design department.
A huge amount of gamers, both casual and core, know that storage might not be a problem the first year, or ever - but maybe one year down the line, you feel you need more storage, also on consoles.
Then it's great to know if the system you just bought have many different choices if you want to upgrade your storage space - and can swap your storage-solution to what you want.