I agree with you here Andrew. I think this type of helmet is realistically probably much safer than your typical bike helmet for the majority of impacts for a few reasons.
The rounded shell, the lack of vents, and the deeper fit and increased coverage. And we are talking about certified helmets here. Not the soft foam/non-cert skate helmets like a cheaper pro-tec or 888.
It's passing the same certifications and then some. And beyond that, it doesn't take much to deduce that these characteristics make a safer helmet than one full of holes with shallow coverage and odd peaks and points and a plastic visor hanging off the front.
I've seen kids smack their heads at the skatepark and be fine, and I've done it myself as well. The round shape is great at glancing off of objects and sliding, and the deep coverage is great at distributing the force over a much larger area of both head and ground rather than concentrating it to a narrow ring around your head circumference or a single point of contact like any of those peaks and points found on "bike" helmets. I can think of a lot of skate crashes where I would have hated to be in a bike helmet as they are so hard and don't extend very far down your head, and those points probably would have ripped the helmet off the side of my head as they grab the ground. From my own experience, crashes and falls happen a lot more frequently in park/pool/DH skateboarding than they ever have on the bike.
Seems like in an environment full of rocks and sticks and all kinds of pointy branches, we wouldn't want a helmet that's full of holes and barely covers more than the top of our head if safety was the biggest concern, but somehow that's the norm.
Maybe we'll all end up in moto-trials style helmets for trail riding in a few years. More coverage than a traditional half shell, smooth and rounded shell that could still be ventilated, flexy visor that shouldn't snag. Might not look half bad without a visor either. Like the Pro-Tec full cut.