Right. A good book on this is Daniel Golden's The Price of Admission. Children of alumni, donors, celebrities, and rich people in general, are favored, as are sports stars. These policies are mostly official but the degree to which they will affect one's chances is not publicly declared.

On the other hand, Asians and the wrong kind of white person are disfavored.

So, the admissions process has some heavy-duty signaling behind it, in contrast to the declared goals. Presumably the admissions policies are intended to let the future alumni signal that they are not just smart but also famous, athletic, open-minded, generous, and rich.

Also on the topic of signaling and top schools: Harvard students are fond of bragging about how little they study, signaling that they are so smart they don't need to.