That's a really good take away for all the people who look down on stuff like this. EVERYBODY cares; they (you) can't help it. Repetitive manipulative messaging (think sexy slim people doing sports in beer ads) works even if you're aware that it's a complete ruse. It persuades your lizard brain and there's nothing you can do about it. This sort of brainwashing is one of the most disheartening and insidious things about human nature and, by extension, the marketing industry.
Don't get me wrong, there's good marketing. There are companies doing amazing stuff and they can tell you about it honestly with a take-it-or-leave-it mentality. It's a noisy world and when enough money gets involved (enough is usually a surprisingly low bar) being honest quickly becomes not good enough.
After spending a couple years in marketing and seeing this kind of research over and over I had to get out. (I left an online marketing agency to focus on design and tech.) I think on some level, it's taking advantage of human weakness. It's in the same ballpark as the studies that show that the placebo effect still works a little bit even if you TELL THE PARTICIPANTS they're in the placebo group. WTF, brain? It's so frustrating.
Anyway, You can bet your life that as much aggregate exposure as the Yahoo! logo gets, that selecting a proven one will impact their bottom line.
It's not a hair worth splitting for your start up with 30 customers, but once you start dealing with billions of slices of attention, shit gets weird and unintuitive. See Google's infamous testing of 41 shades of blue [http://www.nytimes.com/2009/03/01/business/01marissa.html]
