Quoted from DS_Nadine:It's a fact based on your opinion what a vault is.
We have Vaults that are comepletely the same machine (Star Trek), vaults with slight or major additions (Iron Man), Vaults with a completely changed art package (Spiderman).
So the clear definition of a Vault ist: There is none!
Tron released multiple times, changed it's name to "2nd", "3rd", "4th" edition. Changed a bit of stuff like the translite and the bikes, as well as stuff in the manufacturing process like you wrote, but it still is a rerun of an existing game (out of the Vault) that there was demand for.
(It's definately not a different Version to rekindle interrest like AC/DC Luci or Munsters Premium Color.)
Then, I don't believe you meant to imply those Tron 2nd, 3rd, and 4rth editions were in fact different iterations of a Tron VE. Or else, Stern would have called it that way. Those Tron versions came from the same production run, they didn't need to be vaulted. Must have come down to Stern execs telling themselves 'hey, this game is catching and is in high demand, let's do some more and fix a few things along the way..'
You are however right about the lack of a clear definition of what a real vaulted pinball is, because it's all about marketing and selling a niche product that has become in demand. Same goes with Pro, versus Premium and LE. We all have it pretty good idea of what those are, the vault (or VE) is just some different marketing branding.
I went back to Stern's website to read again about their VE releases. In a nutshell, when a game is really successful (and there is still a high demand for it), Stern's goal is '...to take one of our most popular games and make it even better'. Then follows a long list of improvements, affecting every aspect of the game, not just a few decals or a couple of toys. But also music, armor, GI, etc. Same game, different experience.. at least, that's Stern's claim!