I came across something interesting that greatly reduces the impact of this problem (at least on iOS).
When you are viewing a thread, near the top, below "Jump to ...", the title of the tread is shown (with a ">" at the right). If you "click" there, it takes you to that same thread in the browser built into the app. (It even has you logged in if you're logged in in the app.) From here, you can see and view the attachments just fine. Since I find that I no longer have to go search out that same thread in the brower on my own, this is really slick.
So the only remaining concern really is for those cases where the original poster doesn't give me enough context to realize that there are attachments in his/her post. If the app could just give some indication that there are attachments, I'd be happy (which is saying a lot for me :-).