I'll break up the four questions that you put into a single paragraph:

1+2. If we go into semantics, then Splatoon's unlocked content isn't a bonus, but merely the completion of the product you have already paid for.

3. The primary argument against on-disc DLC has always been that you get charged extra for it, so it's $60 plus whatever a publisher felt like charging on top of that. This is obviously not the case for Splatoon, so it's an entirely different situation.

4. If we once again go into semantics, games commonly dictate when you can access content. This includes forced tutorials and mindboggingly boring sections you have to go through before you get to the good parts; or having to beat the entire game on normal difficulty, because hard mode (what you actually wanted to play) is locked. Of course, this is not the exact same situation as Splatoon, but paying for a video game more often than not means that you don't get to play what you want and how you want right away. The thing that is the same across all games, including Splatoon, is that it's up to the individual to decide what is acceptable. Since Splatoon is an online multiplayer focused game, anyone who bought it already planned to play the game for several weeks, if not months. That makes the staggered release less of a problem than it would for, say, a single player game. You see opinions differ; people who play the game a lot would obviously want new content to be released at a quicker rate, but those who only play the game a few hours per week don't get burned out on the available content.

As for your closing remark, and I think this is really your key point, I refer you to answer 3. Splatoon isn't guilty of doing what other games have done in the past.

I said it's not the same. But on the other hand, people who bought and will buy Splatoon after launch have access to more content from the first time they put the disc in. The whole "Splatoon limits the amount of content you can access" debate will be done for by the end of August, because everyone who buys the game after that date won't have to worry about Nintendo unlocking content as everything will already be available.

Do you mean online passes?