Unfortunately I don't have a subscription to the Annals of Internal Medicine, so I'm not sure how their null hypothesis was quantified and tested, nor do I know the dosage that they used, or the duration of the tests. But I'm guessing there are some problems with their study. Of course, for years (and, shockingly, you still hear this line from some in the Anti-Doping Agency) so-called 'experts' claimed AAS had no impact on athletic performance...pretending that skill and 'natural ability' trumped all. Most wouldn't buy this line of reasoning anymore.
HGH grows new muscle fiber (as well as other things), it's one of the few things that can. But it isn't going to do any good unless these new muscle fibers are conditioned and results are going to be much less pronounced (from a performance perspective, you'll still get that general high on life feel-good feeling right off the bat) if you haven't almost maxed out your existing muscle fibers. I used to do (amateur) power lifting and I seriously doubt I could have pushed my bench much above 5 plates without HGH.
So in their study, where these people hitting the gym for 3-5 hours a day 5-6 days a week like most athletes when training. Or were they going about their daily work spending their days at some office job?
HGH may not give you the same instant gratification as Testosterone or EPO, but it will allow you to push your limits and keep growing in the long term.