Again, shooting a .300win mag for 100yrds doesn't give you any advantage over a .30-30... It's just not asking much from your equipment. Shooting a 70 or 80lb bow at 30-40yrds isn't asking a lot either. But if you want pass through kills at 70 and 80yrds, you need arrow weight. Yeah, a 60lb bow can shoot a 420grn arrow, but it ain't going to shoot it nearly as fast as an 80lb bow, so you're going to be sacrificing a lot of trajectory, so by the time it got out to 80yrds, it's trivial, you just don't have the range.
Again, a guy that only takes his bow out of the closet 2wks before season to practice and struggles to punch palm sized groups at 30yrds won't benefit at all (your average bowhunter), but for a guy that bundles sticks at 50-60yrds+, or a guy that could ethically perceive a 100yrd shot on a deer (these guys ARE out there), the difference is real. Whether you or I can capitalize on that difference is an individual aspect that's different for each shooter. I'm not a competitive shooter anymore, and definitely don't group shafts like I did in college (shooting 4 nights a week), but I still shoot well enough that shooting groups under 40yrds means a trip to the bowshop for new arrows, so limiting myself to 40yrds just doesn't make sense.
There's also no arguing that heavier bows perform better on "marginal shots". On a clean broadside shot, no doubt a 60lb bow will deliver a clean pass through. But when it comes to driving an arrow through the far shoulder on a quartering away shot, or punching through the spine on a high angle shot (buck beneath your stand), it's nice having the extra KE and arrow weight. I've had two instances where I had bucks come in quickly and pass almost directly under my stand. I had the choice to pass them up, or punch through their spine. The first time I was set at 55lbs, and my glanced off of his spine and out his shoulder. Luckily, breaking his shoulder blade nearly crippled him and he tried to run across open pasture, so I could track him. The second time I was drawing 75lbs and punched a 400grn arrow straight through his spine, through his heart, and about 6" into the ground beneath him (broke the shaft when he fell on it).