I always found them to be self contained but I feel that way about any solo series for any character. It's the team books are more tricky. "Oh, Iron Man has his old armor on? Why's that?" "It happened in his solo series." "Oh, I don't read that......"
Imagine being a writer and trying to juggle that for 6-7 characters. When you're writing the solo book, you call the shots more.
Most of the solo books seem to exist in their own bubble. For example, even though the Avengers show up sometimes, Amazing/Superior Spider-Man can be read on its own. It was the same easy when I was reading Invincible Iron Man and Wolverine, and appears that way with stuff like Captain America and Thor: God of Thunder.