Well, certainly the taxes as a percentage of the base ticket are high because you got such a cheap ticket. But international taxes are high, and are destination specific. I priced a BOS-SJC round trip, and aa.com quoted me a base fare of $666 and taxes of $106.13 (almost 16%). And it seems that most of these taxes are a flat amount (subject only to exchange rate fluctuations), not a percentage of the fare. According to aa.com, international taxes include:
September 11th Security Fee of $2.50 per U.S. enplanement, up to $5 one way and $10 roundtrip
Airport passenger facility charges (PFCs) of up to $18 roundtrip
Other government taxes and fees (including U.S. government excise tax) of up to $125 based on destination; total may vary slightly based upon currency exchange rate at time of purchase