Steadfast & Gladiators A: You only need one?

Read something that led me to believe that these two enhancements were special and offered global defense even if no more of their respective setes were slotted?

Gladiator's Armor: Teleportation Protection, +Def(All)
Steadfast Protection: Resistance/Defense

Is this correct?

yup. and you can slot one of each.

What Chaos said.

They both offer 3% to all defenses. It is a global enhancement so it will work even if stuck in a power that is inactive when you exemplar down provided you are not more then 3 levels lower then the level of the enhancement itself that is.

PS there is also one in Shield Wall (defense powers) that gives +3% to all resistances if you are doing a resistance build.

Well... The L10 Pulverizing Fisticuffs is rare because very few people want to produce it, not because very few people can do so. The Gladiator's Armor unique (of any level) was originally rare because very few people could produce it. Nowadays, it's less rare but still rare because more people can produce it, but still rare because you can only (intentionally) produce one per character every so many days, no matter how many you might want (or people might want them).

Of course, it has to be both desirable and rare to be as expensive as it is. If you could get a Gladiator's Armor as easily as you can get a Steadfast Protection, it would remain equally desirable, but probably only cost about as much as the Steadfast Protection. Last I checked them, it's about 10,000 times more expensive. I do believe most of that price difference is down to rarity - as far as I know most folks consider the exemplar-friendly behavior a nice perk and not much else, especially now that we actually have ways to produce them at any level we want.