I see no statements of anything altcoin related. In fact, they accept only BTC and USD deposits and you get paid back in the currency you deposited. If this was a legit operation (it's not), then that would make sense if you're only doing BTC/USD arbitrage, because you don't expose your investors to exchange rate risks (which is the whole point of arbitrage, to profit independent of exchange rate developments). Running alt-coin pairs without taking deposits in the relevant alt-coins means that all deposits are exposed to the exchange rate of those alt-coins.

Furthermore, while alt-coin arbitrage can be more profitable than BTC/USD arbitrage, the volumes with which you can make a good profit are much lower, since there simply isn't that much volume in the alt-coin markets compared to BTC/USD and the spread between exchanges tends to go down with increasing volume.

On another subject, the website of BTC-Arbs.com has 4 different names for their operation: BTC Arbs, BTC-Arbs, Bit Arbs and Bit-Arbs. Professional company with 10 employees working out of a Geneva-office? Or just a plain old Ponzi scam? You be the judge.