I had written a whole thing about how I agreed with you, and that this was annoying and should be fixed. Then I figured out a way that you actually can copy, and its actually pretty easy.
You just have to change the way you highlight the text you want to copy.
If you look when you are typing a post, there's a grey box surrounding the text box that has your options and things. Well, at the bottom of that, there's a thing that says 'body' and 'p' and possibly 'div' or some other things. Well, if you click on body, it highlights all of the text. If you click on 'p' it highlights the paragraph where the caret currently is. After you highlight some text in this way, you can use Ctrl-C or whatever to copy it and it works.
Hope that helps you.