You are correct that $1 million in 40 years isn't worth as much as it is now due to inflation. But, it is still worth a lot of money ($262,529 in todays money if historical inflation averges keep up). And $262,529 is more than the average retired person has right now. Just four years of contributions now and he'll do better than many people who had their whole life to save.
As for your "really, really, really optimistic" quote, you certainly are really, really, really bad at math. I gave a fund ticker that has averaged 10.8% over the last 35 years. Then, I said if that historical trend repeats, he'll have over $1 million by investing $20,000 as soon as possible. That is what the math says.
$5000 * 1.1080^40 = $302,385
$5000 * 1.1080^39 = $272,911
$5000 * 1.1080^38 = $246,309
$5000 * 1.1080^37 = $222,301
Total: $1.044 million.
It may be optimistic to think history will repeat itself (I personally use 8% in my own estimations for my planning). But it certainly isn't really, really, really optimistic. Don't like the result? Then reinvent math since you'd be wrong with math as it is.