One reason is that network installs require http. The base system would be unable to self-replicate across network installs without httpd.
Why not FTP? Or even TFTP?
you can do that as well.
FTP is dead.
How I wish this were true.
Yeah, don't you just love how "Enterprise" vendors make it more secure with going with ftps instead of picking a different protocol?
It's very handy to wrap services in HTTP to expose them outside the machine, limiting outside access to a single port with clear FastCGI delegations to specific functions. If you don't build this in, then services shouldn't assume it to be operational and can't auto-configure themselves.
Why is a web server included? It isn't needed by many people!