That was just done because I didn't want to change the extrapolation because the attributes become Epic at different rates, but the item was more designed to show what happened at the higher end IE: past +10, instead of pre-epic.
You know.. I think technically the x10 bonus would apply to ALL the different bonuses - weapon enhancment, ability bonus, natural armor, and deflection - separately. It could be argued either way, since no such item exists, but if you applied the x10 4 times, it would be astronomically expensive at the upper end.
A Good example (not of wealth, but of precise vs Freeform style): In a game I once ran, an evil wizard, in a floating city, wanted artifact X, and threatened to attack the goodly city Y. In a straightforward game, the floating city would be a dungeon, which the players would have to explore and fight all the monsters within until they reached the Demilich at the end for a final showdown. Wanna know what really happened? They blew it up with explosives. It crashed. Demilich died. (again) The End. (Well not really, but the Demilich's plans were foiled by the use of gunpowder, fly, and Invisibility)
rofl!
What I am trying to say is that as the PC characters get higher level, the methods they have for gaining wealth improve as well. By 20th level, If a character doesn't have everything money can buy, then he or she simply is not trying hard enough.
Or the DM is limiting their access to wealth for some reason. But really... do you think a L20 PC could afford a +20 weapon? If he can, something's seriously out of whack.
But by epic levels, gold should cease becomming a medium of value.
I agree that gold itself would lose its value... it would become a trade economy, for the most part - gems, information, magic items, valuable materials (in our world, a d20-sized lump of a metal called arcanium is worth around 10,000 gp), etc. Gold is still useful, however, for things like item creation, spell research, expendable items (arrows, potions, scrolls) that you don't make yourself, paying the lackeys (I don't think the castle servants are going to accept payment in diamond dust, do you?).
Once you get past 40th, though, you've pretty well moved beyond all that - your former henchmen/apprentices/lackeys are nearing (or are) epic themselves, and they've taken over running the castle while you go planeshopping.
BUT, how would you handle item upgrades at this point? Does the DM just say, "Well, you're 45th level, let's upgrade that sword now", or can the PCs do it on their own (hey, they've got tons of gold! They can afford it!)? The former seems kind of artificial and silly ("Ooh, next level I get a feat, an ability bonus, AND a weapon upgrade! Yay!") but the latter has its inherent problems too, unless you institute a hard rule about item bonus being limited by ECL, and not just a guideline formula.