The only "problem" with that system (Thornir's) is that you're on a slippery slope to the scenario in which having a magical weapon confers no bonus over not having one.
Irda Ranger: The "Memory Item" flavor you're proposing seems pretty much in line with some of the stuff in Weapons of Legacy... or at least a subset thereof. I actually quite like it from a narrative perspective, since it replicates Campbell's convention of the hero's magic weapon in the game: that is, Durendal is attributed its "unbreakable" quality because of its relationship with Roland, Excalibur becomes symbolic of Arthur's own military might and his ability to heal national differences, etc.
Of course, as with many flavor elements, it's something that seems rather campaign-specific (and arguably campaign-determinative), although you addressed this in your reference to an implied setting. I would certainly love to have something like this, but wouldn't mind if the DMG also included a few other flavor options for how magic items "work."
My own thought is that I will continue to play without numerical bonuses of any sort from magical weapons when making the transition from Iron Heroes to 4e. IMO, it makes more sense to give magic items only basic equipment bonuses (higher hardness, hp, and break DCs), and to put everything else into the realm of powers. For certain DMs who don't like quasi-magical martial powers, for instance, one could put stuff like the fire-related Desert Wind maneuvers (or whatever their 4e equivalent might be) into the weapon rather than the character. Just assume that such weapons can be imbued with those powers in off-stage rituals, or offer weapons imbued with the appropriate powers in a treasure hoard, depending on the style of play you want.
IMO, flat +x bonuses should just go into the character, not his stuff. Flat bonuses lack flavor; they screw up the power curve if doled out or acquired piecemeal; and to my mind, they duplicate nothing in fantasy except D&D itself. Making Andúril a sword with a ghost touch and an undead command power seem to me much more in line with LotR than the sword making it easier for Aragorn to hit orcs.