If you gave it to all classes, the glaring problems would've been revealed within an hour. By giving it to an obscure subsection you lengthen the time it takes to find the problem.
From a person who has designed surveys for the purposes of exposing problems, you don't target one particular audience, you target the broadest so you can get immediate feedback from a diversity of people.
Then it would have taken a month or two to fix nonetheless. Would you like a MONTH of this abuse from EVERYONE?
What you are saying makes sense, although think about it. Everyone will defend things that make them better. If everyone had the ability to do this nudge, then the feedback would be jaded and corrupted.
So they gave it to the least common class to get a more honest response. (Not saying all of it is honest)
EDIT: I would also like to add that finding problems in programming is a lot different then finding problems within a community. With programming, it is better to test small so that only small changes need to be made at a time to get things right. It is better then putting in every program and then erasing all of it. Sure, you get feedback faster. Although it will still take longer to fix. (We all know how slow they are already ;p)