I've often argued that what matters in terms of opening-weekend box office, at least for a sequel, is less the sequel (whether it's good; its buzz; its Rotten Tomatoes score) than the previous film in the cycle. Positive feelings will lead to bigger box office, negative or “meh” feelings lesser box office.

If so, “Iron Man 3,” shouldn't have opened well since “Iron Man 2” is hardly beloved. Even though I liked it.

But I knew “Iron Man 3” would open well and it did: It grossed an estimated $175 million in the U.S., the second-highest opening weekend ever after “The Avengers” $207 million gross last May 4.

And I knew it would because, for most folks, the previous film in the cycle wasn't “Iron Man 2” but “The Avengers,” which also starred Robert Downey, Jr. as Tony Stark/Iron Man. And that movie is beloved. And that got them pumped for this one.

Or it could simply be that it's the first weekend in May and people want to ride that roller coaster again. It could be that we're all well-trained and Pavlovian. First weekend in May? Superhero? Pant pant.

The U.S.'s salivary glands are hardly unique, by the way. Worldwide, “Iron Man 3” has already grossed $680 million, which is already the biggest international hit of the year. (Any guesses at No. 2? Answer in the comments field.) It's also the highest international gross of any “Iron Man” movie. That's right. “Iron Man” grossed $585m in 2008, and “2” grossed $624m in 2010. The majority of that money, for both movies, came from the U.S., but now the rest of the world is going to “Iron Man,” too. Now the rest of the world is as well-trained as we are.

In other non-news, “Pain and Gain” was No. 2 at the box office with $7.6 mil, and “42” was No. 3 with $6.2 mil. “Oblivion,” at No. 4, fell off 67% and appears to be living up to its name. It'll be outgrossed (at least in the U.S.) by “42,” a baseball movie, which I doubt many foresaw.

No other movie besides “Iron Man 3” opened wide this weekend. Studios aren't stupid.

The numbers.

America got off the couch this weekend.