I think the article short changes the value of startups that can be described as a specialization of another. There's lots of differentiation that can happen in a single space across verticals. Think about what features are important to people who use Word vs. Latex or Blue Nile vs Amazon.

The other thing I would add is I got some advice (which I now agree with) from a college professor that business should focus on being really innovative/risky in one dimension, not in all. This seems like a good way constrain the areas your business will really be innovating in.