That's the reason commonly given in the US, too, but it's not entirely true. Faxed signatures have legal precedent as being legal signatures. There are laws that state that electronics signatures in general are legal, but they vary from state to state (though most are equivalent), and I don't believe there is any case law backing up what, precisely, an "electronic signature" can be.

Ultimately, businesses tend to take the legal safe road of faxed signatures.