And I agree, there's nothing wrong with the older designs. In fact a lot of dome tweeters simply mold the dome and "surround" out of the same material for exactly the reasons you mention.
The problem with foam is it's not very resistant to the elements. It's fine when protected. for example, when you remove a speaker from the cabinet, the foam compression gasket is always in good shape. I have a friend in Hawaii who had to replace the foam surrounds on his JBL's every 30 months on a regular basis. They just rotted away in the heat and humidity!