No, the logic is that it helps in low-speed falls and accidents, but it makes drivers more likely to hit you and doesn't really help much if do. So maybe it's better to wear a helmet--I'm have to look at the data more. But it doesn't seem obvious what the answer is. Here's a statistic:
700 bicyclists died on US roads in 2007. Over 90 percent died in crashes with motor vehicles.
What sorts of crashes though? There's getting hit by a car going at 50mph (goodbye world) versus, say, clipping a car door as it opens and going over your handlebars.
In the former your survivability is suspect even with protective gear, in the second I can see a helmet come into real use.
700 bicyclists died on US roads in 2007. Over 90 percent died in crashes with motor vehicles.
http://www.bhsi.org/stats.htm