What's noteworthy about Exchange is all of that comes together, in one package, with documentation, that integrates with your existing MS domain users and groups that manage desktop and server access, with a support contract from a single vendor, and as much as it sucks, it generally "works". Plus you can put up a job listing for 2 Exchange admins, and get folks who know how to configure/maintain the whole system.

Trying to build all those services yourself using open source options, tying them all into an LDAP server, is an amazing pain. Does everyone need all of that? No. But honestly I can't imagine trying to handle the mail, shared mailboxes, messaging, scheduling, booking resources (conference rooms, equipment, etc..) for a Fortune 500 using the other options I'm aware of.

It may be "blather" to you, but it's generally pretty important stuff for a large company.