Since we're used to them, we're also used to trusting that most of the time we'll be safe making transactions using them. Credit cards, including the risks and costs involved, are part of the consumer's daily life and the store's business model. So part of the reason we trust credit cards is simply that the system and the companies involved are well-known. We know that generally we can expect to use credit cards without major problems. The idea of electronic cash isn't new, but no company has managed to make an e-cash system both convenient and trusted.
Convenience is a difficult issue for online money because it's new.
There's no way to get around the fact that every person who uses an e-cash service must set it up. Even worse, without a standard e-cash method, the online consumer might have to sign up with several services. PayPal has attempted to reduce this problem by using existing systems. You can create a PayPal balance using a debit or credit card. Once your account is established, you then use it to transfer funds without using any plastic.