You don't just "call up" Tony Stark and have him help you out. He's notoriously self-absorbed, there's virtually no chance he'd even take your call most of the time. Even putting aside the fact that in Iron Man 3 he effectively retired all his suits, the situation in Winter Soldier here developed way too fast to call some robo-man from New York in to help out. It'd take too long for him to get there, the communication itself might be intercepted by HYRDA, there's an established "don't trust anyone" thread running through the movie, etc. Tony Stark isn't actually part of SHIELD in the first place, he just helped out in New York that one time.
Just because other heroes exist, it's a pretty big stretch to assume you can just page one and have him show up for any random crisis.
I agree and I'm not arguing that he
should have shown up. Stark is self-absorbed, so if you tell him there are three giant warships going up in the air that are planning on shooting him dead (which, given their accuracy in shooting Falcon, might not be a concern for Iron Man) he might be inclined to help. If not by suiting up, maybe with some legacy Stark Industries weaponry, I don't know.
What I'm arguing is that you say something like that. Have Cap say "Shouldn't we get Stark involved here?" to Nick Fury in the secret bunker and have Fury explain it away in one line. It doesn't even have to make the most sense, but at least you're addressing that you've thought about it!
Reaching out to other Avengers -- however that would be done -- would kind of defeat the purpose of going underground. One of the reasons Steve and Widow are able to find a safehouse with Falcon is because he's not on anyone's radar. He's not an Avenger, he's not with SHIELD, no one is suspecting that their prime target is hiding out with some random VA worker.
Besides, Hawkeye is likely on a mission, Thor in Asgard, Banner is in the wind somewhere. It's not like these guys are all within reach.
Again, I'm not arguing that any of it should have happened, but that it is addressed. When they go "underground", have a quick quip about "Guess that means we can't call your old buddy Hawkeye, huh Black Widow?" and her saying, "Nopre, we're on our own."
I can create a logic in my head for why a lot of things happen, but as a film goer in a straight action movie, it's better for me not to be wondering why someone is or isn't doing something and just having it explained. That way my mind is just sitting back and enjoying the excitement of the action.
This is why I brought up maybe needing to see IM3 and Thor 2 before seeing this movie. Lots of stuff going on in the other film franchises that could have subtle impacts on this film. And I definitely agree that I probably see it differently than the characters in the universe do. But that's their problem!
Again, I'll leave it at that. We can go round and round about why or why not. Just something that came to me as I was watching the film.
Oh, on a different topic, the digital aging on Peggy, while technically well done, totally pulled me out of the scene, though I did like Steve's line about "a dance from his best girl". That was very nice. But every time I looked at her, I was noticing the digital lip movement. Just get some prostethics next time!