I don't think this is true at all. To start with, there's roughly 2000 years between the earliest known philosophers and the analytic-continental split. Plenty of philosophy majors can and do get really into the ancients or medieval philosophers or whatever and complete their degrees without doing much more than a cursory read of the major thinkers post-Kant. And anecdotally, my own undergraduate degree was in philosophy, from one of the more prestigious schools in Anglo-Canada, and we had plenty of opportunities to dive into the continental stuff.
Once you get to the graduate level and academia folks focused on Derrida or whatever are going to gravitate towards the universities that prioritize the schools of thought they're interested in, and those have always been on the continent for the continentals naturally. But for run-of-the-mill philosophy majors in the Anglosphere, IMO you should just assume they have a reasonably broad and just-deep-enough knowledge of the entire history of philosophy and make no particular assumptions about their interests.
td;dr: I think you give Anglo philosophy students FAR too much credit. In my experience they aren't well read at all and their departments are staffed by professors who aren't well read.