You can't teach 'aptitude' but I think you can encourage those things i.e. reading, curiosity, exposure.
You're right though that rich kids probably have a huge advantage in prep for Eng in terms of the former, but whether or not you call it 'classist' is besides the point: teaching your kids to show up to class and pay attention, do homework etc. is not something that costs money (of course it can help).
"So if you think it's some kind just/effective/correct that these kids are kept out (just because they don't have good essay writing skills or something) well I have to wonder if you're just someone trying to keep the labor pool small to inflate your own salary (or for other reasons...)"
For a PhD you're having an odd bit difficulty with leaps of unsubstantiated assumptions, because there's definitely nothing in my statement that would remotely hint about 'What I'm trying to do' about anything. I mean seriously, "I'm trying to keep the labour pool small?" What?