My take is that some boots are better suited than others depending on the terrain. Take, for instance, the Montrail Moraine ATs vs. Kayland Vertigos vs. Keen Targhee IIs.

The Morane ATs are heavy-duty, super burley, boots. However they aren't insulated and as stiff as full on mountaineering boots. I've used these when carrying heavy loads in off-trail terrain. They fit my feet well, are super stable for carrying heavy loads over rocky terrain, and the leather is premium treated so as to be waterproof in wet conditions without needing a membrane (3mm Perwanger Leather, best available). I would use these when backpacking into the Wind Rivers or any mountain range that necessitates a long approach if carrying a heavy load.

The Kayland Vertigo's are excellent general purpose boots that are best for weeklong backpacking trips where the weight of the pack is kept around the 30lb. mark. They are stiff, but not too stiff as to be difficult to walk in and, because of this, they don't need alot of break-in time (this break-in time is needed for stiff boots to force them to flex where your foot flexes and for the leather to shape to your foot--depending on the boot, this make take only a few days all the way up to a few months). I love that they are full-grain leather, but fairly light. I also love that they use an eVent w/b membrane, much better than Gore-tex. These are my favorite boots currently.

The Keen Targhee II boots are more a 'hiking' boot in that they feel like a burley pair of athletic shoes. The leather isn't as stiff (split grain vs. full grain leather), it uses EVA foam rather than polyurethane for weight and cushiness (the EVA does wear out much faster than PU and isn't near as stiff), it is much lighter, it doesn't have the rock protection of the two previous boots, and my foot does get fatigued if I am carrying more than 25 lbs. eight miles or so. I can tell a huge difference between these and the Kayland boots in terms of comfort and support. I think this is the biggest difference...

Trail runners would most likely be next on the tier which are best if the load carried is around 15lbs. on an established trail. My feet really become fatigued and sore if I do many miles in these shoes if the trail is rocky and I'm carrying a lot of weight.

I would base my decision on what type of activity you will be involved with. If you plan on backpacking a week or more in rough terrain, you are best suited with a boot like the Kayland Vertigos. However, if you are an ultra-light backpacker (pack not more than 15lbs) who goes for weekends on intermediate to mild terrain then trailrunners might work for you. If you mostly dayhike in the Rocky Mtns, the Keen Targhee IIs are excellent. This also depends on your feet's characteristics (high arch, bunions, sensitive feet, etc.). I would seek out a good specialty shop who knows footwear intimately. Good footwear is expensive but can be one of the best investments you will make.