At that level you are not using the card for credit, but rather as a replacement for cash. And who wants to write a check when you can use a credit card instead?
It's faster and safer to use a credit card, plus the merchant doesn't have to worry that the check will actually clear.
And using a debit card when you have a lot of money in your account is not safe. So credit card wins.
And for that same reason dwolla will stay rare for such transactions - without the consumer protection laws that credit cards have people will just not use it with strangers.
It will be used exactly as the article describes: To send money between people who already have a relationship, but it will rarely be used for purchases.
Basically he's replacing checks, not credit cards.