Both spells are Line effects, meaning that they run from a vertice to a vertice.
The Blade Barrier, being a damage dealing line effect, affects anyone in any square the Line touches. Or, more simply put, it isn't a pen mark on the board with zero-thickness.
So with that in mind, imagine three straight rows on the battle mat:
AAAAAAAAAAAAAAAAAAAAA
BBBBBBBBBBBBBBBBBBBBBBBB
CCCCCCCCCCCCCCCCCCCCC
I can place a Wall of Force along the "top" side of row C (Bottom side of Rob B, same thing).
I can place a Wall of Force along the "bottom" side of row A (top side of Row B, same thing).
Now I place Blade Barrier diagonally along the length of B, from top-left B to bottom-right B.
There is no square anywhere along B, within the length of the spells, that isn't in the area of effect.
That's the ugly layout.
If I wanted to get technical I could lay my Wall of Force spells along the "Top" of A and the "bottom" of B, and the Blade Barrier along the straight line where A and B meet. Now I have a 10 foot wide path that is all within the damage area of the Blade Barrier.
The "Ugly" layout, it could be argued, couldn't be laid out because the target(s) might extend outside their squares by way of 40 inch blades, etc. The rules don't actually allow for that (Medium sized creatures use a 5x5 square, period), but I'm playing to your argument here, so we'll presume that that's an actual consideration. The "Ugly" layout also doesn't leave the target any room to sidestep the barrier, thus making it possible to rationalize the "No Save Possible" scenario we both agree shouldn't happen.
The more technical layout takes advantage of the rules for Line effects, but allows for a credible possibility of a Save in the form of a side-step, as described in the rules.
And to be clear, the tactical movement rules in D&D 3.* pretty much do make it a tactical-skirmish game. Miniatures and battle mat are *NOT* optional for encounters like this, and figures really do have to abide by the "snap to grid" rules.
Now, to be clear, you can't use this to force characters, be they PC or NPC, into that area, nor drive them into a line.
This works most easily when dealing with a single target, or perhaps two. (Two points define a Line, after all, and we're dealing with three parallel Line effects). If you happen to be able to trap more than two in there it's a happy accident.
And, as I said earlier, when you're at the level where you have enough spells to throw four-spell combos like this (with one of them being the ninth level Time Stop, any target worth dropping such an expensive combo on is almost certainly going to slip right out of it. If they can't then you probably blew your big-nasty on the wrong target.
So this is a thought/rules exercise and nothing more.
Your arguments so far have fallen into two basic categories: "It's not fair to deny them an escape", and "In the real world sense, people take more/less space than this would work on."
My reply to both of these is: We aren't in the real world, we're talking game rules. "Fair" isn't part of the consideration of what's possible under the rules.
What a DM will or should allow, either for PCs or NPCs, on the other hand, should always take "fair" into account.