Heh, unless someone stole my quote as their own, that was me (I think talking to Quis way back), and it was specific to SD vs Kensei.
The reasoning is that by switching stances / gear / etc. you can raise your AC by well over 20 points as needed as a SD (5 CE, 6 shield vs. shield wand, 5 blocking, 4+ armor boost for example). By having the ability to raid buff into the 90s, you thus have the ability to be into the 70s in DPS mode. That way you can tank anything on normal in full DPS mode, and slowly trade DPS for AC as needed for harder difficulties or when buffs are sparse.
If all someone cares about is normal, then sure, probably any decently geared SD could "tank" ToD normal or whatever, but being able to switch as needed is really the only thing SD has going for it - a well-geared Kensei would probably be a better tank than a poorly geared SD. I think that was also around the time when I ran a Shroud with no less than FOUR people intimidating and blocking Harry, so I was a little frustrated with SDs wearing shields all the time and boasting about a 60 AC in defensive mode :P
Edit: and to get slightly back on topic, I remember the days when 200 HPs meant you were pretty much invulnerable - you could run into a pack of beholders and have enough HPs to survive a failed disintegrate. Good old Invaders before they screwed up Enervate...