As for email--yes, there are hundreds of alternatives, but somehow we keep coming back to email, and when we need to guarantee that somebody else can communicate with us, that's what we use. I've had Skype updates break. I've had Google Chat randomly disappear or be inaccessible. I've had AIM clients (of many varieties) die on me. Email, barring the normal issues you see with it, is always there.
This is completely false in my experience.
1) Businesses use wikis all the time. The last 4 places I've worked at have had department wikis. This includes a University, a Mega-Bank, a family owned e-tailer, and a medium-sized consulting firm, which hits just about every size business you can have aside from "start-up".
2) Getting a wiki set up is trivial. For the large companies you request the IT side to give you a VM and an address on the intranet. For the small companies it's usually a spare box and an address on the intranet. It's dead simple.
Also I suspect you would be surprised at how much leeway managers have in choosing collaboration mediums. Email is the old standby, yes, but many managers will choose other ways to collaborate within their department. Most businesses have an IM server for internal chats as well.