Exactly what do you mean by that? To me, that means they never reject you, and you are just supposed to take the hint when classes begin and you still haven't heard. I don't think that's what you're talking about, however.
The simple answer is that the really good schools don't leave you hanging, and let you know as soon as they have made a decision, even if it's 5 minutes after your file is complete. Those schools are far and few between. Many, if not most, schools hold off on sending out Rs until they are done sending out IIs, or even until after they are done sending out As, which isn't until at least May or June for most schools. This really isn't a silent R any more than a school that doesn't do rolling admissions has silent As, or silent WLs. If they communicate it eventually, it isn't silent, even if they don't communicate it as soon as a decision is made.
If you haven't heard from a school, it either means: (i) you haven't been reviewed yet; (ii) have been rejected but not yet told; or (iii) have been put on hold to possibly be looked at again after they have gone through the entire pool once. If Rs have gone out and you haven't received one, you're either in bucket (ii) or (iii). If no Rs have gone out yet, you can be in any bucket.
Bottom line -- silent Rs are rare, and don't happen until the end of the cycle. Regular Rs happen throughout, and, of course, have already happened at every school by now, even though most schools have not communicated them yet. There honestly is no way to know in the beginning of November unless you have been told, so there is nothing to be gained by worrying about it. Just try to hang in and be patient. Other than the rare superstars, the rest of us are all in the same boat.
