The first reason is reliability. Unreliable software will kill your business and drain your bank account, no matter how much money you save by using it. You can't afford inaccurate results. At ArbitrageBoss we are fanatical about keeping our servers in tip-top condition and quickly fixing suppliers that break or change their page structure.
The second reason is productivity. Time is money and our real-time interface allows you and your staff to get a lot more done in less time without waiting for pages to load. There's no point in saving money if it sucks up your expensive time instead.