I suspect the opposite is true. Mostly IIT CS/EE majors get into the top CS PhD programs. Many non-CS folks, sure change professions to being programmers but rarely graduate with a stellar PhD from a top 5 (10?) computer science program. Most of these IIT grads have to apply to graduate school with 6 semesters of work. Without a CS/EE degree, and a recommendation of a top IIT CS prof (who has a good reputation of sending top students regularly to graduate programs) whose students get pattern matched by the selection committee's from top 10 CS schools, it is next to impossible for a non-CS IIT grad to compete with a typical top 10 graduating CS grad (9.4 + GPA, probably some Math/Phy/Chem olympiad medal or ICPC finalist/winner, almost perfect GRE scores, may 1/2 ACM conference papers). Please note that I emphasize the top 10 CS schools part quite a bit because the game of finding an asst prof job is heavily rigged and top 10 CS school grads have a major advantage over others here.
Thank you for clarifying. In hindsight I think you're right. There is a higher burden on the foreign student. An MIT EE or applied math undergrad with a lot of CS classes can get into MIT's Phd program without the CS degree, while it's tougher from someone unknown to the faculty.
