I'd honestly go ahead and bite the bullet and say these students are lacking in an important intellectual capacity if they can't handle that extremely modest amount of abstraction. If they are successful it is probably due to a solid work ethic.
You know, that's what I thought for the longest time, but I eventually saw enough otherwise-perfectly-normal adults get hung up on the same problem--- and talked to enough other teachers who reported the same thing--- that I came to believe that there was something fundamentally different going on, and that it wasn't just a few tough students.
As somebody who's been programming for most of my life, it was really hard for me to learn to think about this stuff from the perspective of somebody who'd never seen it before. Many thought patterns and cognitive skills that are second nature to us programmers are, for a lot of people, very difficult to learn.
