Look, Doctor Proctor.
I'm willing to endure your flippant tone, but don't gloss over legitimate issues, alright?
I have already made it clear my post was only a nitpick. But now it seems we need to go to the bottom of this.
If I want to create a +2 plate mail, you say I have a choice between standard PHB plate, and AV masterwork plates.
But what choice is that?! I could either get a straight +10 (8+2) or get Rimefire plate which also gives +10 and resist 1 all. Or I could, for the same price, get Layered plate, which gives +11 AC!
Where is this "mundane armor with a higher AC but no bonus" you speak so lightly of?
I see nothing simple about this. Instead, I find it to be confusing and indicative of power creep.
I'm not being flippant, and the only one being an *** here is you.
I simply mispoke. I didn't have my AV book in front of me and assumed that the tradeoffs that apply to the armors at the higher enhancements applied at the lower ones. I was incorrect. There's no reason to be an *** about a mistake though.
The point I made still stands though. Your
DM can hand you +2 Mundane Plate if he feels like it. Or he can give you Rimfire. He can also hand you +6 Tarrasque, or +6 Godplate. The Tarrasque has Resist 5 all, but lower AC than the Godplate. So you get hit more, but have Resist 5 to any incoming damage from those hits (as well as auto-damage and ongoing damage effects that aren't affected by AC).
Now, if you're enchanting the armor yourself? Yeah, it would be silly not to make one of the AV Masterword Armors at the +2 or +3 enchancement level. At +4 and beyond though, it depends on what you want. Do you want more AC, or less AC with a bonus?
And as for power creep, so what? It's a +1 to AC or a NAD (or Resist 1 for Plate) at levels where a lot of players complain about AC anyway. The old power curve for AC was very bumpy, and general had some issues in the Paragon tier. Now that's been fixed. It's not putting your totally out of line with enemies of those levels, so I wouldn't call it "power creep" just because there's a bigger number there.
To sum up though, Masterwork Armor is easy to understand. Anything above a +4 enhancement bonus is automatically Masterwork. If you're using the Adventurer's Vault then you can also get Masterwork Armor at the +2 or +3 enhancement levels. It's up to your DM to determine if this is automatic, or if you can still find mundane +2 or +3 armor. It could either way really...but it's the DM's decision.