There are a lot of great services out there -- many of them free -- that make it easy to produce HTML emails, maintain email databases, let the user know how many people open each email, etc. Those sites typically provide templates and very simple interfaces that allow for sophisticated, professional emails to be developed quickly and easily.
Another great feature is that they are set up to send out emails and avoid spam blockers. Let's say you want to send an electronic newsletter to 1,000 customers. If you were to do that with your HTML email editor, the chances are good that email would be blocked by your own server as bulk mailings are typically viewed as spam.
An HTML email service, however, effectively sends emails one at a time so as to avoid that problem. For that reason alone, one of those services might be your only option for sending bulk emails. Thank goodness there are a lot of those Web-based services out there and they are competing for customers.