Google should sent plain text mail with format=flowed (http://www.ietf.org/rfc/rfc2646.txt) as that would fix the issue for both very old clients which profit from the hard line breaks while still providing word wrapping on mobile clients.
It's ok if they don't support it when displaying mail, but by just setting that flag on sending, people with good clients will get the best possible experience
Because they are being used? (In turn because they tend to be the best ones around, most of the newer email software tends to be crap if you go by productivity rather than shininess.)
Also, this is not just about compatibility with old clients, but also about compatibility with old emails. If you redefine the meaning of previously used email syntax, that changes how old emails get displayed, which sucks if you have an email archive that goes back more than a decade.
Gmail doesn't support format=flowed, so from that perspective, it too is an old client. Last time I checked, one of the most widely used non-web clients also didn't support it (Outlook).
But the good thing about format=flowed is that even if a client doesn't support it for display, it'll still look good (on desktops)
It's ok if they don't support it when displaying mail, but by just setting that flag on sending, people with good clients will get the best possible experience