A coworker and I have been talking about 16:9 vs 4:3. Our main audience and market has older tv's. I favor shooting 16:9 and converting to a 4:3 letterboxed layout, he favors straight 4:3.
Definitely 16:9- 4:3 is completely outmoded. HD formats don't even have 4:3- only standard definition.
Also in terms of DVD authoring it's a universal format. Once you create in anamorphic 16:9 a 4:3 DVD player/TV will automatically letterbox. With 4:3 you're essentially shutting out anyone who buys a new TV today. Or rather forcing them to look at your footage with huge black bars on the sides. Here's some details to help you convince your partner: