Oddly enough, this resonates, however how can a claim like this be supported? It can't. Seemingly small UI changes, which might appear to fall in that "last 10%" category can require immense research and iteration to achieve.

This quote should be restated: "10% of variation in features can account for acquiring 90% of market share."

In other words, seemingly small variations in features tend to lead to product differentiation. This does not however mean that simply refining your product a little bit more will get you the runaway success you are seeking.