Mike, interesting topic.
Personally, I've never had a penetration issue with big Snuffers (the 1 1/2 inch ones) on animals from deer, pig, bear sized up to moose and elk sized with bows in the "moderate" range - say mid 50's to mid 60's - EXCEPT those that would have been non-fatal anyhow - mainly a couple of high-loin shots that did not enter the chest cavity, and were not on a trajectory to do so even if they had penetrated farther, and a followup center shoulder blade on my already fatally wounded moose. The only animal I've shot in North America with a Snuffer that I did not get very good penetration was my musk ox, and I got to the offside ribs on him (2 times). That was the hardest/tightest rib cage I've seen other than on a water buffalo. That buffalo, and 4 big pigs in Australia, were the only animals I've ever shot with a 2 blade head (STOS) - 75 lb bow and 1100 grain arrows. Penetration was a non-issue on the pigs, obviously, and recovery distance averaged about 15 yards. In my limited experience though (say 6-8 pigs) I've found them to be VERY easy to kill. Not even in the same league as a whitetail, maybe that's just my experience.
Alot of this, as you stated, may be partially attributed to shooting animals at the right time. This is probably one of the most overlooked aspects of bowhunting - the learning when is the "right" time to drop the string. I know guys that have bowhunted seriously for decades that still can't get it figured out, and I have known a couple guys that were just naturals, instinctively able to get the job done. Its a combination of the animal's mindset, your mindset, the situation, and lots of other variables. Eventually, just like any other "woodsmanship" skill, it becomes second nature. I suspect that guys switching over from compounds where they may be used to "drawning down" on deer way before the animal enters the shooting lane may have a VERY difficult time learning this with a traditional bow.
Now my wife and I HAVE had quite a bit of experience over the last couple of years tracking deer for people with our dog. The vast majority of these guys are "modern" archers and the heads of choice seem to be very small, steep angled, 3 blade heads. Penetration has not been a problem on the tracks we've went on..full pass thru's are the norm.....but the distance the deer travelled has been AMAZING sometimes - of course we don't get called on deer that are hit properly in the first place. That said, I've never had a deer fatally shot with a Snuffer go over 300 yards if he wasn't pushed - and I've made some hits I'm not proud of. But these little 3 blades - even through 1 lung and a liver - have given us 800-900 yard tracks. I've been shocked at some of these tracks, this would be unacceptable to me. I question the hunters about sharpness, and I don't think that is the issue as these come pretty sharp (replaceable razors)- and the guys that call us are generally pretty serious hunters, I don't think they are shooting animals with arrows they shot into the dirt first....I think it is just the little hole they make.
R