There seems to be far more awareness about this recently. We stopped feeding grapes about 2 years ago, when we read something about their possible toxic effect.
Anyway, as it intimates on this link from the ASPCA, until just a few years ago feeding grapes/raisins was not uncommon, and not seen as something to worry about unduly.
I'm not sure if I'm allowed to post this link, but just in case I am here it is....
http://www.aspca.org/site/PageServer?pagename=grapes
I've also seen similar articles on other US dog-sites which specifically ask that we dog owners tell as many people as possible about this potentially fatal danger. Thanks to the original OP for raising the awareness!