Why exactly is that "discrimination" and not, you know, simple evaluation? Is every company that doesn't hire based on a random number generator discriminating?
That's not Jane Street's process at all. I know first hand people from schools you've never even heard of that got internship offers, and I also know first hand people from MIT that got resume screened out. I'm not going to claim that there is no school bias at all, I don't know the finer details - but it's definitely not explicit as you describe. There are a lot of comments all over the internet (including this thread) from people at non-target schools that were interviewed.
There are some trading companies that do seem to legitimately do that kind of filtering (Two Sigma's application has a drop down menu for school with like 10 options and then "Other", DE Shaw asks for your SAT score, etc.). So I can see where the idea came from, but it's not true of JS.
In the trading industry, DE Shaw and Five Rings are the two places that care about school prestige well into someone's career. All other firms don't give a crap about it once someone has some experience.
I went to a crap school in India and a mediocre US school for my grad work, still got interviews at trading firms as a new grad and an industry hire. Currently working at one right now, so I can say that I have seen it first-hand.
I have proof otherwise that can probably be replicated if need be. I can DM you the details. Granted this was a few years ago so hopefully they've matured since then.
...as opposed to give every person a fair chance based on merit.