I'm not sure of the point you're trying to make with cash on the internet. Businesses accept CCs online, and they still pay a fee. If online businesses want to accept BTC and convert it to something else, they're going to pay a fee.
And not that you are the only one guilty of this, but I'm tired of the "but bitcoin is this" statements whenever it seems to apply in the most beneficial way to make a point. Lots of people believe bitcoin is the second coming of currency, and I'm just pointing out that it is going to have an incredibly difficult if not impossible time trying to fulfill that role. No, the deflation aspect and 21 million limit don't really mean anything if bitcoin is mostly just a payment processor with a few speculative nerds hoping to make money on volatility here and there.
The point that you're missing is that bitcoin isn't just a payment processor. It can function in that role for a very large portion of it's economy for decades, but that isn't it's only use. CC's & paypal have no other use and therefore those transaction fees are truely unavoidable. With bitcoin, there and will be many different wasy to exchange. In teh early stages, yes, any bitcoin accepting business is going to have to deal with the exchanges & the costs that they can impose. This will limit early adoption rates. However at some point (usually aroun 12% of the general public in any given area or market) bitcoin is suddenly 'mainstream' and the savvy business owner doesn't have to depend upon the exchanges for all of their conversions. I'll concede that a future that involves never needing to deal with the exchanges if you are a bitcoin business owner isn't going to happen in my lifetime, but it's all a matter of degree. These are not sudden events, they're transitions. The business owners who deal with bitcoin early on are as likely to keep a portion of those funds as not. No business just hangs onto checks or credit card receipts on the possibility of appreciation or the possibility of reduced conversion costs. Such things will never happen. Again, bitcoin is much more than a payment processor, even though that is a large part of it's current functions.