Vick, well, in essense it IS the exercise making me stronger... It is the stimulation of resistance training, and then of course resting those muscles for a few days. It is the RECOVERY time that I have a hard time accepting! In my type of training, i.e. not going to failure, I find that two days a week of heavy lifting is sufficient and progressive.
And yes... Great progress!!! You can tell your arms a little thicker. I think it all really depends on your goals, though. For instance, as a personal trainer, I wouldn't reccomend this protocol for somebody looking to improve their functional strength and power. I still strongly stand behind focusing on the basic movement patterns: pull-up, push-up, press, squat, deadlift. These necessary movements cannot improve without practice. Have you ever tried a traditional weight lifting day, just doing setsxreps?