Prices were manipulated once a secondary market sprang up—and they continue to be manipulated—but the collecting of comic books began when some collectors started buying them off of the stands in the late 1930s, before a secondary market even existed, when most people were just throwing their comic books away. That's the difference.
In the case of Signature Series books, CGC basically invented that hobby by creating registry sets, giving more points to Signature Series books than to Universal books, and declaring that books with autographs on the cover were not to be penalized grade-wise whereas no one 30 years ago would have considered a comic book high grade if it had an autograph on the cover; it would have been considered defaced.
If you had told me back in 1993 that you had gotten the cover of a comic book autographed, my first thought would have been that you had some actor or actress autograph a dollar-bin comic with a photo cover. No one would have sought an autograph on the cover of a valuable book. (I'm sure someone here could post an example to prove me wrong, so let's just say that it would have been very uncommon, shall we?)