For my game, we actually differentiated between "artifacts" as defined in Ascension, and artifacts or magic items as defined in the core rules. We call the Ascension artifacts "Soul Objects," and just posit that every one of them could be used in a manner like that described in Chapter 1's Resonance section (not that my PCs have ever bothered).
What happens, then, is that the
practical difference between Soul Objects and artifacts/magic items becomes that Soul Objects automatically grow with the user/creator- and other items don't. So yes, you can go get that
+20 Universal Energy Blast Vorpal Greatsword when you're ECL 60, but that same weapon's going to look pretty shabby compared with your Soul Object weapon when you become, say, ECL 120. And you have to spend actual XP, materials, and time to upgrade an existing item- Soul Objects just automatically change for free whenever your ECL goes up for any reason. Soul Objects, therefore, are limited to 4 as described in Ascension; other items are not.
Belzamus makes a good point about Uncanny Weapon Spec, too.

If they're actually
nonmagical, then as long as you can afford the materials cost of creating/getting them, I say go for it.