it was in EVERY ES game and Fallout 3/NV dont know about 1/2 or tactics
NV didn't have a lot of leveled stuff though, most vipers, scorpions and fiends all have static spawns, same with most coyotes, nightstalkers, radscorpions et cetera.
Only leveled places I've seen is Black Mountain, Deathclaw Promotory and after advancing the main quest enough Legion and NCR spawns are different.
Other than that it does not really follow the scaled to player level thing.
FO1/2/T did not have it either, it had designed that around Klamath you will meet gecko's in random encounters, but even if you're lvl 50 you won't meet fire gecko's.
Fire Gecko's only spawn in the area south of Klamth/Den and north of San Fransisco.
So it had a different system of random encounters.