This is not 100% true. 05s, which are not MDS, have a recommendation of 5W-20.

 

My 2500 08 has a recommendation of 5w20. Its written on the oil cap and in the damn booklet!!!
I don't like 5w20, I think its too thin, and not that great for our winter conditions. That's one reason why i'll never buy a hemi with MDS...