At the risk of being pedantic it begins "If you're serious about increasing your strength, follow this six week training program and you'll soon be on your way to completing 100 consecutive push ups!"
If you're interested in increasing your strength you don't want to be doing a hundred of anything. For most people you need endurance from the waist down and a shitload of explosive power from the waist up.
True, paddling a kayak, digging a trench, and some other things need endurance in the upper body, (speaking as someone who did silly numbers of press ups) I think I wasted a lot of time, and didn't do my shoulders a load of good either.
Having said that, impresses people
I think 20 good pull ups from a dead hang is a better goal. In the real world you'll pull more than you push.