In Snow Leopard, the first time you ran a Rosetta app, the OS prompted you to install it to run the legacy application. These users, if they are running Snow Leopard already got a warning.
Any many of them won't remember seeing the warning or installing Rosetta a year or two later. I'm not talking about the users who read MacRumors and similar sites and are well aware of the issue - we're a minority of the installed base.
It's funny that Apple's OS 10.6 help page on Rosetta installation has a link to their "Rosetta website." Clicking on that link redirects to Apple's main Mac page.