They certainly scale in cost akin to D&D items, but not in utility. D&D magic item utility barely increases. A +6 sword is pretty much just a sword, maybe with a dinky trick, but I think a stealth bomber can accomplish quite a bit more than a pistol can.
Again, my problem is that 4e magic items are unimpressive. Why not have a figurine of wondrous power that turns into a harrier jumpjet inscribed with runes and possessed of a malevolent sentience.
OK, let us consider swords then:
I'm sure you can buy today a serviceable but by earlier times standards rather crappy sword today for say $500.
You could buy a better sword, maybe actually made to something like standards of weapon quality considered ordinary 500 years ago for probably several thousand dollars. Lets say $4000
You could buy a genuine medieval or Renaissance weapon for probably what, $20,000 maybe, I don't know, but it wouldn't be cheap.
You could buy a genuine ancient 13th Century Katana of high quality, but it would surely cost you 100's of thousands of dollars. Say $100,000.
You could buy the finest sword in existence today, but it would SURELY cost you millions of dollars, say $1,000,000.
The sword Kusanagi simply cannot be purchased for any money. Bill Gates entire fortune would not even tempt it's keepers to sell it or even show it to you.
Sounds like there's quite a range there. Remember, these swords are all pretty roughly of the same utility. Maybe the cheapest ones would not serve so well, but they sure aren't as much different as magic blades are in 4e.