Mutual intelligibility is rarely the only reason for calling a different langauge different. E.g the scandinavian langauges are relatively easily mutually intelligible, so is Czech and Slovak, yet they are called different languages mainly for political reasons. On the other hand, many of the Chinese "dialects" are not even alike, yet they are still considered one language for political reasons. Even perhaps more familiar "Black English" is usually considered to be nothing more than English with bad grammar, even though it's very clearly a distinct language of its own, that is not readily mutually intelligible with standard american English.