Welcome to the world of internet mail. It's been like that for 30 years or so, but you're probably not the last one to realize that it's broken.
Onkel Paul
Actually, e-mail has been around for a bit more than 40 years: See http://openmap.bbn.com/~tomlinso/ray/firstemailframe.html and http://en.wikipedia.org/wiki/ARPANET
It's true that e-mail phishing is a somewhat newer phenomenon (about 20 years, see http://en.wikipedia.org/wiki/Phishing), but the prerequisite is that sender information can easily be forged, which is basically built into e-mail protocols from the beginning.
The only way out of this would be to widely use public key encryption and signatures. Most people don't think their e-mail communication is valuable enough to warrant the additional effort, though.
Onkel Paul