Consumer rights mean something to me so I don't want to willingly give them up. Being able to own the games I buy is important to me.
Download games would be fine if they were DRM free (GOG sells DRM free download games) but Nintendo puts a lot of restrictions on their download games, so you are paying more for less if you buy them. If you buy them, you are part of the reason there are so many problems with modern gaming.
Unfortunately for Smash, even if you buy the physical copy, you won't get the full game. Balance updates, Mewtwo, the Miiverse stage and anything else they add in the future will have DRM so no one can own it. 10 years from now if someone buys a used physical copy of Smash Wii U, they will be stuck playing the base game with unbalanced characters. As a retro gamer, this upsets me. I understand that all of these updates are free so I guess I can't complain too much about them but they still have a negative affect on retro gaming and consumer rights.
On a related note, Amiibo is basically a physical version of DLC (if that makes any sense), and while it is absolutely horrible to have to spend over $600 to have full access to the game that you bought for $60, at least this content can be owned.
The exception to this would be online only games, like MMOs. I can understand why those games would completely cease to exist after several years.