jdrakeh
Front Range Warlock
Generally when I hear "High Magic vs Low Magic" I'm thinking of the relative amount of obvious magic appearing in a campaign setting, such as the vague sorceries of Hyperborea vs. the flying ships and lightning trains of Ebberron.
I think you and I are on the same page, so to speak. For me, the divide between "low magic" and "high magic" is about the availability of magic in a setting versus the magnitude thereof.
Frex, I consider Arthurian Britain as depicted by Malory to be a "low magic" setting, as magic of any notable consequence appears to be known and tamed by three individuals (i.e., Merlin Ambrosious, Morgan le Fay, and Nimue) in all of known creation and magic items seem to similarly be limited to three known examples (a sword, its sheath, and a grail). And monsters of magical origin? We have a few scant mentions of dragons (mostly metaphorical) and the Questing Beast. The magnitude of the magic in Malory's version of Arthurian Britain is incredibly powerful — but it is also incredibly rare.
Conversely, I place all official D&D settings save for Dark Sun into the realm of "high magic" due to the common nature of magic. Most D&D settings are dripping with magic right out of the box. Entire economies are built around magic items, monsters of myth and legend seemingly outnumber normal animals, clergymen are assumed to channel magic from gods by default, and so on. While it's true that magic in D&D is not the epic force of destiny-shaping power that it is in Malory's Le Morte d'Arthur, it is far more commonplace and often unremarkable as a result of this saturation.
The idea of increasingly more powerful magic items isn't a huge issue for me in a game predicated on an adventuring economy that assumes the killing of monsters, collecting of treasures, and rising through the ranks of fame. I love "low fantasy" gaming, mind you, but I have other systems for that. For me, D&D is pretty much the anithesis of "low fantasy" and that's why I love it. I mean, 'cmon — this is the game that invented "leveling up!"