From my perspective, the only people to whom this is a big deal is those who somehow managed to convince themselves that Nintendo is "above" this sort of thing.

Judging by the sales of the handheld Mario Golf games, it's not like they're affecting a particularly large number of Nintendo fans.

It seems your logic is "do things the way they've always been done or Nintendo fans will be upset".  In which case, I am surprised there are any Nintendo fans left after we've had a guinea pig dual screen handheld; guinea pig 3D handheld; guinea pig motion control console and now guinea pig tablet console.  All of which are much longer term investments than a game which may or may not be the tipping point in terms of future business decisions.

I'm stretching this example a bit, but you're basing your whole argument on the assumption that Nintendo fans are loyal to a t yet would jump ship the moment the first new business direction is taken.  An assumption which can neither be proved nor disproved without trying.  But I'd imagine one title will not be the tipping point; if it's the first in a line then it will be.

Nintendo with Day One DLC?! Quite strange to say the true, specially for Nintendo, I just hope they don't pull this with Mario Kart 8

The price do seem okay, 5.99, for 2 new courses with 18 holes each plus a character, it sounds like a good amount, specially if you buy with the Season Pass, 108 holes and 4 characters, for 14.99, seems like a okay price, a bit high, but not extremely high. Atleast they are letting you try it out before playing.

:/

You don't need to buy it without knowing. I'm planning on buying DLCs for TLOU. I want the two multiplayer mack packs, the weapon packs and the single player DLC. Now that they are all out (or at least announced in the case of the second multiplayer DLC), I know I want all of them. The single player one is US$ 15, the first map pack is US$ 10 and the second one will probably be the same price (or maybe higher because it includes the weapons). The season pass is US$ 20 so it's what I will get. 

In the end season passes aren't bad. You can get all DLCs with a good discount. 

Technically, the game is not developed by Nintendo.

That's not how it works. A game is a project as any other so its costs (including each work hour for the entire dev team, use of PCs and other equipments, marketing and distribution) must be lower than the full revenue from the game's sales. The time used to develop a DLC is costly. If it was to be included in the game, maybe they simply wouldn't be able to do it without exceding costs. So DLC actually is a way for the user to pay more to get more content. It doesn't matter if they developed it before the release, it was made because they knew its costs would be separated, not included in the main project costs.

people are saying the game is cheaper than usual 3ds titles and the news says the game comes with the same amount of holes as usual mario golfs. So, instead of looking really bad, it just looks a little bad.

I think they are doing it because the game is 30$ not 40-45$ like a normal 3ds game.
I fucking hate DLC as a whole but atleast they have the decency to make the game cost less.

Oh if this happens in Mario Kart 8 gaming as I know is dead forever.

See third parties, this is how you offer DLC. You create a full game and add completely new content that is fully optional and relatively cheap.

You don't create the game and then strip stuff out to make DLC.

Hopefully Nintendo continues this as they have done similar on WiiU with Pikmin3, NSLU, and hopefully future WiiU titles yet to come.