I think all this talk about the legality of using such services misses the point. It's about legitimacy, especially that of state leaders. While the western media might try to use it to delegitimize some non-western leaders, the leak actually works both ways.

Any country leader who'd make a speech to tell her (or his) people she doesn't care about them or their country, would do nothing illegal, but would probably loose her power. It's the same here - the leak serves as proof that the national Elite in many countries is no longer "loyal" to its imagined community (aka nation).