Doesn't GROUND SPEED play a role in figuring glide ratio?
I get that it plays no role in best L/D speed and such, but if you want to figure out whether you can make the Azores or whatever from 37,000 feet, don't you need to know if you have a tail or headwind component?
Seems to me TAS is irrelevant. IAS tells you how to fly for the best range/glide ratio possible, and GS tells you what that ratio will be (and whether it will be enough!)