Phones, like mail, are a special case in a whole bunch of ways, legally, is my (Not A Lawyer) understanding. Using them as a basis for comparison is probably not going to reveal a lot.
Well we were talking about expectations here, were we not? I certainly expect my IM, email, VoIP and other forms of communication to be no less private than phone or post. So does, I believe, nearly everyone else. Just because one stumbles (stumble is not the right word though for what article described - the malicious intent was clear) into an unsecured segment does not make it right to eavesdrop.
Do you not picture a distinction between a landline (non-cordless) phone and wireless internet?
By 'trivial' to tap into, you mean I'd have to physically cut your line somewhere and attach a listening device, right? It seems very reasonable to expect privacy on a physical point to point wire.
With Wifi, if you're my neighbor, I need to sit at home with my computer and your photons come straight to my antenna. It's like you're giving them to me. I don't see the similarities.
A landline phone is also trivial to tap into. Should you not expect some degree of privacy on the phone?