I think that it's a bit backwards to ask to not copy copy specific things. The "sender" should typically put all available representations on the pasteboard. It's up to the "receiver" to decide which one of these representations that it would prefer to use when pasting,
I don't agree. The syntax highlighting is applied in the development environment because it has meaning there, and also because the user has set up a color scheme that guarantees legibility there (although Xcode still fails to ensure legibility when it highlights lines).
When pasting into another app, it's apparently not possible to change the background color of that application to ensure legibility. Therefore the user should have the option to copy plain text from Xcode. I think this option used to exist, or I've seen it in another development tool that does syntax highlighting.
Copying from Xcode, then pasting into a plain-text editor, and then re-copying and pasting into another app is a pain in the ass that can easily be avoided by offering this common-sense plain-text option in Xcode.