Some of these are pretty good questions. I'll start with the easiest.
6. * suffix denotes globals. It's just a convention, may be violated in some places.
3. Yes, you could use +. The arc codebase is like others in that it was added to over time, and you can see the evidence for that. In this example, + probably didn't support lists until after w/uniq was implemented. Other examples are new syntactic sugar that hasn't spread through the codebase (http://arclanguage.org/item?id=10974)
Update Another example of arc's non-uniform implementation: functions like copylist, map1, pair could be shorter by inverting the condition. I can't help thinking I'm missing something there, though.
4. At first glance, reclist also returns a list suffix rather than just an element.
Your version is less general, but if you keep finding yourself doing f:car perhaps there's a case for a variant.
2. Is there an example where the current version is broken?
5. I'd be very surprised if an iterative version bought you much performance, with all the other inefficiencies in arc. Also, it's kinda pretty to imagine recursion implemented by iteration implemented by recursion.. :)
