Well- I don't know that "most" homebrewers recommend using a starter. Certainly not in all cases (me, for instance). It depends on what beer you're making. A Wyeast Activator (NOT the Propagator, which is designed to be incorporated into a starter) or a White Labs tube is designed to be pitched directly. All dry brewing yeast I know of is designed to be pitched directly (hydration is usually recommended, but I've pitched Nottingham and S-05 dry with good results).
That being said, these things are all designed for 1) 5 gallon batches and 2) as the directions you cited state, wort at <1.060 OG. In the two years since I began brewing, I have used mostly the Wyeast Activator, with three or four dry yeast batches, and several starters, made from Wyeast Propagators. All of these produced good beer. However, I'm thinking about making my first barleywine this coming Winter, and you can bet that I'll make a big starter to get that going.