Starting a business using bitcoin as payments is a good start since it has no overhead costs involved like credit cards do for each and every transaction made.
If you directly accept Bitcoin without a third party in the middle to convert your transactions to fiat directly, then yes, there aren't any fees involved since you get the full amount.
However, the far majority of the businesses prefer that third party in order to avoid dealing with the volatility. It's not nice when you sell something for $100 worth of BTC, and the next day it's only worth $90. That's a direct loss for businesses.