modern 5.2 FI roller engine cylinder ridge ?

It's all of it. Better oil. Low tension rings. EFI.

Basically, the reduced fuel-wash (removing oil from cylinder wall after the piston descends) from the EFI allowed the low-tension rings to work, which could then be made thinner since they weren't using their own spring tension to seal. Carb swaps on late-model motors can run the rings to the junk pile pretty quick if you're not careful.

I ran Mobil1 in my Neon that finally topped over 400K miles before it swallowed its' own intake valve. Too bad the valve guide can't hold up like the bores. That motor didn't have any ruing ridge, and the bearings looked pretty darn good too.

I'm not afraid of any untouched Magnum motor. Run that thing and don't look back.