is this true about processors?

Every processor from a given line is identical, the 2.4ghz, the 2.6ghz, the 2.8ghz...Intel makes 1 chip, but due to manufacturing differences not all chips behave exactly 100% like eachother...so they are binned into different bins at manufacturing based on inline manufacturing tests. Most of these manufacturing tests are VERY strict so even if a processor fails one out of a million tests it gets binned with non-pristine silicon, some silicon skew towards the slow side, some towards nominal(median), and some are faster..its just how silicon manufacturing works. So they take the fastest ones, and make them the high clock rate. The other lower ones they artificially cap them by locking their multipliers among other things. They are identical and in most cases fully capable of behaving like the fastest ones, but to be safe Intel/AMD artificially cap them.

Therefore in overclocking you aren't really "overclocking", your restoring it to its true potential because in the real world that 1 out of a million failure is not going to be noticeable...granted in some cases people are pushing it well PAST its potential with insane voltages and water cooling.

There is binning, yes, but the primary differences that I'm aware of are going to be multiplier unlocks and cores. Sometimes you can unlock locked away cores, sometimes you can unlock multipliers. Overclocking is pushing the component in question beyond its intended use. This is especially true when multipliers are locked, because you are increasing the clock speed in a completely different way than the manufactuer had intended--so in this case, no you are not "restoring" anything, but using it in a different way altogether.

Overclocking has changed dramatically in the last 10 years (as long as I've been in it). It went from being extremely complex and dangerous to your components to nearly idiot proof (my motherboard OCs for me automatically). So that plays into what you're talking about as well, the technology has changed a lot.

Yeah, JoT has covered it all pretty well