Yes, the real type signature is more difficult to read, which is why there are use cases.
Anyway, I have looked into it, and verified that there's no CanBuildFrom that creates a Range. Furthermore, it seems $Coll (as opposed to $coll) is only used on use cases, so IndexedSeq would be better. Or, perhaps, just do not redefine it on Range (I'm not sure if it gets inherited from IndexedSeq or not).
It's a very small change, but one does have to build the docs to look them over, and I'm a bit out of time these days. Maybe someone will come and pick this up, but this sort of ticket is very low priority. If you had more experience with Scala, I'd advise to look into submitting a pull request for it yourself. And if you have enough git, github and ant experience, you should try it – just remove the line where $Coll is defined on the source file for Range, plus do all the fork/branch/edit/test/push/pull request work. People on irc and mailing lists can help you with it.