Today, thousands of firewalls are deployed to limit a company's exposure to the Internet. These firewalls are fairly set in their behavior and have become a barrier to new Internet applications. These new applications want to traverse the firewalls. So, Internet-application vendors are using HTTP as a shortcut through firewalls. There's nothing new about picking an underlying protocol, or substrate, for an application based on market pressures.
Technical rationalizations are always available to confuse the issue.
Be prepared to face significant pressure to accept any of them just to move forward. First, there's the familiarity and mind-share argument. It's easier to familiarize programmers with HTTP than train them on a newly created protocol. Then, there's the compatibility concern. The self-justification is almost comical.