I have seen a glass roof on a Scion (Toyota Yaris) last month. Why would that be difficult? Secondly, the retracting door handles have always been a "Wow" point, and seem to be quite in demand for the Model S. I also see some skepticism for 19" rims, when it seems to be a factory option for many upper end cars. Why would Tesla, considered to be competition, not have a glass roof, or retracting handles, or a 19" option? I think you folk are wrong.
It's not so much that a glass roof is difficult, just expensive. Same with the door handles. Renault may prefer to go with a design that is tried, tested and less expensive rather than to spend extra time and expensive on a handle that may increase risk of defect.