It always mystifies me that some people object to Americanisms. What's the point? There isn't just ONE English in the world any more, there are LOTS of Englishes...Indian English, Singaporean English, Carribean English, Australian English and so on. Each has its own vocabulary, grammar, pronunciation, abbreviations etc and there is a constant flow from one to another.
I would never say or write 'math', but I have no objection whatsoever to anyone who does. If anything - being shorter - it is a more effective abbreviation than 'mathS'.