Well, this IMO is an issue with english. In german, Austria is spelled Osterreich (for example). In german, it is very common to call a country a land/empire (reich) of "nationality": Deutchland (Germany), Frankreich (France), Russland (Russia)...

How do you know if a significant number of countries or states end in "a"? Is it more than 30%?

Cliff, great question! I had never thought about it. Does it have something to do with ancient languages, like Latin? But I'm not sure what "Florida" or "Libya" have to do with Latin.