That's what I thought, I don't know that e-mail is still the best, but it's at least what I thought most people at most places still use to do exactly what you described there.
It's not perfect but I do think it's the best for a number of reasons:
It has the lowest barrier of entry (I don't have to train people/myself on how to use the e-mail GUI), don't have to sign up for some new account, don't have to rely on some other company's up-time (or potential dissolution), and don't have to pay a subscription fee.
A company I'm working with now insists on using their Basecamp account as our means of communication and it's certainly less convenient than e-mail would be, and (at least to me) it doesn't provide any features that e-mail doesn't as far as interoffice communication goes.
