I actually have a exhaust shop at home. The new cars have flex pipes mainly because they are front wheel drive and the engine twist up and causes major vibrations and will break the welds and joints if they are not installed. I have installed flex pipes right off the headers on older cars and i dont see a difference in vibration as long as you use good hangers.
This sums it up , cars with transverse mounted engines have flex pipes, I can't say I seen them on conventional mounted engine configuration.
