I believe the poster was referring to this. Generally speaking most DP's are setting on an air-ride suspension. That's why most DP drivers love their ride. A gasser could be outfitted with an air ride and probably ride as well except for the fact that 95+ % of gas coaches are on the F-53 chassis which has straight font axles which ride awful.
Also consider this aspect of a lot of the diesels They have independent front suspensions I believe. If they do then that is an additional reason they tend to ride better.
TeJay (Tim) Auto Instructor 35 yrs (4-yrs USAF) Liz: RN/ WBGO 2014 Vista 30T/ F-53/ CHF/5-Star/Koni/Centramatics * Bella- Golden/Cocker mix & Louie-The cat / All Retired