Online transaction providers, like Liberty Reserve, Paypal, credit card processors, your bank's website, and so on, are really not digital currencies at all... they are transaction processors.

Bitcoin, and things resembling it are actual cryptocurrencies and something we could truly call an e-currency. It's about as trackable as cash (in that it can be tracked but it takes very significant effort, and it can be traded like cash.. it's much more than a number in some database.)