16:9 is pretty much universally accepted as a production format everywhere these days.
If you are making a DVD, then make it native 16:9. The same for web video. Broadcast deliverables are of course 16:9 in HD, and 16:9 in SD in digital formats in many markets, 4:3 deliverables can be converted however you wish. (Letterbox, or center-cut).
When shooting 16:9, it is best to protect all the critical content within the center 4:3 safe area as often downconversions cut the sides off.
well, there's a difference between the aesthetics and the technology. you can letter or pillar box any format within the 16:9 frame that broadcasters require. 2.35:1 is indeed a very popular format for promos.
They'll be shot 16:9 widescreen then cropped to various degrees for the look that gives. E.G. They might be croped to 2.39 to look like a film or even 3.00 to look super wide.