Measurable is certainly a better term that could have been used. "Not insignificant" itself should be reserved for unmeasurable topics. Pain is a good topic for the discussion of "not insignificant" because pain can be ambiguous and related contextually in the "of the moment" kind of way. We can talk about how a pain can be intrusive, however in degree of displeasure it is minor. An intrusive pain would be not insignificant when the pain is reoccuring, much like the papercut reference. In the case of something that can be measured in mathematically relevant terms we should say "marginal" or talk about the average battery savings across the board.
Anyway, we're getting off topic the article states "although the difference is just 17.7W and 3.8W for CRT and LCD respectively" and we can see that's a significant amount of power. Particularly for the CRT monitor, 17.7W we're talking about quite a few watts. CRT monitors are almost certainly reserved for desktop environment rather than laptop, however power savings come in the form of money alone, rather than battery life. I would be interested in laptop measurements as the article is only related to desktop monitors. I imagine the 3.8W is much closer measurement towards what a laptop would give us. Laptops can run on 60W without much trouble and I could see 3.8W being important.