The generalisations are repeating patterns (empirical laws) about how buyers buy, and how brands grow. I don't understand why you would say this doesn't apply to small companies? Or small brands? Their buyers buy in the same way, they compete in the same world.
For example, the empirical pattern that brands mostly have very light, occasional customers (who largely buy other brands). One of the charts shown is for Coca-Cola, a big brand chosen deliberately to make the point - i.e. if this is what it's like for Coca-Cola imagine what it's like for smaller brands! It doesn't take much imagination to realise.