I'll quote a sample of the guy Zak was talking to/about. And I'll highlight the important part.
THe way I see it is, I want to have maximum control over the encounter difficulty so that when my party fights a BBEG or other major battle, I can be reasonably sure that they're not going to end up steamrolling it or being TPK'd unexpectedly. In my experience that's not really fun for the players or the DM. To me a lot of the drama from combat is sometimes coming down to the wire. Who is going to win? I want to be able to play my NPCs and monsters to their fullest without either wiping the party or being slaughtered, unless of course that's the purpose of the encounter.
The guy wants complete control over whether a TPK happens, which is to say he wants to make sure a TPK does not happen.
You can actually see the contrast in Zak's post
Zak S - Exactly! I want to be able to play my monsters and NPCs to the fullest knowing It MIGHT lead to a TPK!
You can see the difference between "without" and "might". But even Zak's "might" is problematic.
So, here's my comment:
You do know this guy is trying for the illusion of death/a TPK, by having a system which is so fined tuned it appears your going to die, but actually it's so fined tuned you wont. He just can't admit that, he has to say "I want to better gauge the results". And why does he need to better gauge them/know them in advance? So he can pick the one where the group doesn't die.
It's a recurring phenomena in gamers. I've had this chat with a friend of mine where he was doing everything to stop a PC from dying, yet when I suggested we just acknowledge PC's can't die, just defeated, he couldn't stomach it. And here's a link to another, with the guy quoted. He has a million reasons why killing PC's sucks, yet he can't get that that means PC's will never die (the system certainly wont force him to kill a PC - so if he hates killing PC's, when are PC's ever going to die? Never. But he couldn't admit that).
Not that your own approach isn't potentially problematic
Sure they sometimes steamroll or get TPK'd (maybe 10% of the time)
So let's say a TPK happens 5% of the time. So after, on average, twenty fights the whole party dies and everyone makes new characters? Predictably? So you'd never really make double digit levels, let alone top level. That kind of conflicts with the high levels. Which if your cool with that, okay.
Or does TPK mean one guy actually gets away and arranges some recover or resurrection? Or even if no one gets away, res's can still occur? In these cases the K in TPK stands more for Knock Out than kill. TPKO.
The death thing is a problematic issue (which leads to gamers like the linked guy, who can't admit they are attempting to have the illusion of being able to die, while fiercely demanding rules which will avoid death occuring (always by an apparent skin of the PC's teeth though (though on serious analysis, its not at all skin of the teeth)) or you just get a TPK predictably after X amount of combats. It doesn't matter if it's a 1% chance of TPK, if you do around 100 combats, you eventually die.