I agree, and I think that's especially a good argument for email. For mail submission at least, I think most users for that use-case are now either using or moving to encrypted SMTP AUTH with certificate checking, which should be fairly robust on the local side (between you and your ISP/company), modulo the problems that exist with the CA system. For IM though I think lots of people are more worried about embarrassment than crime: someone grabbing & posting your cybersex logs online; or your comments about office politics (or an affair, or whatever) being read by snooping IT staff, that kind of thing. Some people specifically use IM for office-politics stuff rather than email, because they assume (probably correctly) that IT staff can more easily pry into their email.

Of course for that use-case you don't really need end-to-end encryption: an encrypted connection to the IM server would be fine, and maybe actually better. But a bunch of services don't support that (though Google Talk does).