I think the contrast shouldn't be with rethinking fundamental assumptions, which is another good but rare activity. It should be with assuming that things are pretty much as good as they get, or assuming that small wins aren't worth bothering with. Because that's where a lot of businesses are all the time. Computer hardware is very much the exception.
If you want an example of where this matters, the car industry is a great example. In Rother's "Toyota Kata", he has a graph showing productivity per worker among big auto firms. The large car companies all rise together until the 60s and then plateau. Toyota, which had a very strong focus on continuous improvement just kept on rising for decades. This enabled them to go from Japan's post-war decimation to become the world's largest car maker while the others stagnated.
And I should add that continuous improvement is a good way to drive fundamental rethinking. The only way to get long-running continuous improvement is to pay a great deal of attention to how things actually are working. Eventually you will say, "Well, now that we've solved a bunch of little things, the biggest bottleneck is X". But changing X forces fundamental reevaulations.
For example, consider software release. Unreleased software is like inventory just sitting around the factory. You've paid money to make it, but it's not earning any money for you.
Years ago, quarterly and annual release cycles were common. The last part of the cycle was when a large, manual QA team would beat up the whole product. As we have kept squeezing release cycles, this has forced all sorts of innovation. At my last couple of companies, we've used continuous deployment, where every commit to master is automatically tested and deployed to production. These small teams averaged a few releases a day and had no QA people. Etsy has 50+ releases a day [1]. If you were to describe this to people 20 years ago, they'd call you insane; it's a fundamentally different view of how software gets made. But we've gotten there via 15 years of continuous improvement.
[1] http://www.infoq.com/news/2014/03/etsy-deploy-50-times-a-day