They are intentional. Without the code block formatting, the results of the R session get quite jumbled. If you want to see for yourself, check out the docs compiled from current master. I don't know why it was changed to a period here (it's fine in 1.x), but the "::" is the way to go. The public docs (1.x, right?) correctly render this as a code block (as of right now, anyway):

http://ipython.org/ipython-doc/dev/config/extensions/rmagic.html

This is the kind of thing that would likely get caught more readily if someone accepts my "fast docs make target" pull request (#4208)!