As miroslav notes, in the long run, noise reduction is dead (as everything is, in the long run). But in the now-anachronistic short-to-medium term, it is the case that dbx was pretty common in prosumer gear but quite rare in consumer equipment. It was all over Tascam stuff, including reel-to-reel tape decks. In a full-on pro setting, I think it existed, though was less common as it was less needed on 2" decks running at 30 ips. Consumer decks generally had Dolby.
Reasons:
- Dolby was more tolerant of consumer-esque sloppiness, like playing a Dolby-encoded tape without any decoding at all, or the wrong flavor of Dolby. That hurt the sound quality, but it didn't sound as out-and-out wonky as playing a dbx-encoded tape without any decoding (or with Dolby decoding). Consumer users will tolerate (or, sometimes, not even notice) moderate impairments of sound quality, but are impatient with adjustments and things you need to think about to avoid your music sounding flat-out "broken."
- As in other similar cases (like video tapes), there's a tendency for the industry to go with a single standard, so the equipment makers don't need to make multiple variations of their machines (and license the technology from multiple patent-holder) and the content publishers don't need to sell mutliple versions of their releases, and neither has to deal with people who bought the wrong flavor and are mad about it. That tendency isn't as hard and fast as some people make it out to be, but it does exist.
- Brand-name recognition. Once Dolby got a foothold, it became something the market recognized was "good" and was readily identifiable by name (unless, of course, you called it "Dublin," or maybe even then).
