I'm really only familiar with movie-verse, but I tend to write movie-verse Steve with a slight healing factor. So when a burning house falls down around him, it still keeps him out of the field for a month, but not as long as it would take a normal human to live. I also seem to like having either Steve or Tony end up in the hospital for something or another in my fics, so they have to be able to be hurt that badly in the first place. XD

For Tony... I enjoy playing with the arc reactor, but I also tend to go with what we see, and what we see doesn't include RDJ acting like he's in pain for three movies for having the reactor. So I tend to tread softly on the effects the arc reactor might have on him. That stated, I have just written an entire fic based around Tony's health issues after the reactor is taken out, so there's that. They do, after all, state that no one has survived the open heart surgery technique performed on Tony before, so it's been interesting playing with what could happen after the arc reactor is gone and the shrapnel is gone too.

Plus, who doesn't like making Tony think he's dying again? XD