1% price difference. Subtract trade fees. Then divide by 2 (because you need BTC on the high-price exchange and the same value in USD on the other). That's the theoretical profit if you can utilize all your funds. In reality, you'll have most of your fiat stuck moving through the slow international banking system from one exchange via your bank account to the other exchange.
If you can translate a consistent 1% price difference between exchanges into a daily 0.2% profit then you're doing an amazing job.
Apart that I used to see greater differences than 1% most of the time between btc-e and bitfinex, there is no need to divide by 2, since btc-e is all the time the lowest price, so the operation would consists just in sending fiat to btc-e to buy btc there while selling btc on finex at an higher price.
Of course you need to divide by 2. If BTC is at $500 at the cheap exchange and you want to arb-trade 1 BTC, you need 1 BTC on the expensive exchange and $500 on the cheap exchange to perform the buy and sell orders simultaneously. That's $1000 worth of funds you use, split between USD and BTC. If the price-difference is 1%, that's $5 profit. That gives you a profit of 0.5% of the total funds involved in this trade ($5 on $1000). Of course you need to deduct $2 in total trade fees for these 2 trades dropping the profit down to 0.3% of the total funds involved in this trade.
[edit]: and of course there is no need to use the banking system for each single trade, just to refill the fiat deposit on btc-e when needed, which may be once per week or so.
To me it seems feasible. And probably a pro with high volumes could even obtain lower fees.
If you refill "when needed" or "once per week" that means you have a ton of money sitting around doing nothing for most of the time. As you mentioned, arbitrage opportunities are almost always in the same direction. So if you buy on BTC-e and sell on Bitfinex, any fiat you have on Bitfinex is idle and doing nothing. The same goes for any funds that are in transit in the bank system. But this is still investor money and counts towards the total amount invested. That means that all these idle funds drag the profit further down.
There are further issues with the claims made by Bitcoin-Trader, but the above alone should be more than enough to convince people that the profits claimed by Bitcoin-Trader, more than 1% almost every day, are unrealistically high.
So wake up and smell the roses: There is no trading going on. Your deposits pay the profits for earlier investors and new depositors pay your profits. Just like any other Ponzi / HYIP scheme. And as long as people keep depositing, the site will keep paying and everything appears fine. But like every other Ponzi scheme, eventually the new deposits will dry up and the whole thing comes crashing down.
