Was the paid market for RSS readers really that big before Google Reader? There were tons of free readers (as you say, it's a pretty simple product to make). I don't remember any big-name paid RSS readers.

NetNewsWire was huge if you were a Mac user, and was released in 2002. NewsGator had a Windows app and paid syncing service, and bought NNW (it's changed hands a few times, now at Black Pixel). Both of these predated Google Reader and were paid apps.

There are also plenty of paid apps in the mobile space that sync with Google Reader.

To give this some context, Brent Simmons (the create of NetNewsWire) was discussed by The Economist in a 2004 article.

http://www.economist.com/node/2476892

RSS aggregation is simple to replace, but feed browsing history and the search might be impossible to replace.

Try http://rssident.com

Browsing history and a bunch of other features are still being added to the UI but search already works.

If the web had been as unpopular as RSS readers, things might have been different. In a health market, if the leader fails to innovate, competitors come in and steal share.

In an unhealthy market that's not growing any more (like RSS), things get a lot more stagnant because folks aren't actively making product choices any more and there's not a lot of incentive for new entrants.

I'm betting there's not a ton of innovation in the Gopher market, either.

Gopher is now in its post-apocalyptic "Thunderdome" phase.

An "application layer protocol designed for distributing, searching, and retrieving documents over the Internet." RSS? No. That's a description of Gopher, from Wikipedia.

I just realized something... RSS is the new Gopher.

That description also describes HTTP, SPDY, and a bunch of other protocols. Relatively speaking, RSS never achieved the kind of popularity. Back in about 1993, there were more Gopher sites than HTTP sites.