I don't see the official announcement at Mt.Gox's site though despite the claims. Only link is the ticker data though.
Someone has clearly added these tickers at MtGox, if an incorrect pair is used you get an error :
For example this URL :
https://data.mtgox.com/api/2/LTCBTC/money/tickerReturns this :
{"result":"error","error":"Unknown currency requested","token":"invalid_currency"}
While this URL :
https://data.mtgox.com/api/2/LTCUSD/money/tickerReturns this :
{"result":"success","data":{"high":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"low":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"avg":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"vwap":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"vol":{"value":"0.00000000","value_int":"0","display":"0.00\u00a0LTC","display_short":"0.00\u00a0LTC","currency":"LTC"},"last_local":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"last_orig":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"last_all":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"last":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"buy":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"sell":{"value":"0.00000","value_int":"0","display":"$0.00","display_short":"$0.00","currency":"USD"},"now":"1364820419218936"}}