There are now 1,000,000,000,000 threads about oil that all answer these types of questions but I will answer it. You are risking stiction in any season if you use dino oil. non-sythetic oil creates varnish in the injectors thats what creates stiction.
I don't believe that statement to be 100% correct. The stiction issue, atleast in my opinion is caused by certain additive packages not able to withstand the HPOP.
Even though lube is speced CJ-4 from one company to the other there are differences, sometimes major differences, in the additive packages.
In my own 6.0 experience, I've been driving one since early '04, I have never experienced "stiction". My current '07 had three OCI's of syn 5w-40, other than that its always had dino, same as my '04. I have NEVER used an oil additive of any kind either.
I am always amazed at everyone on the syn bandwagon, feeling that its "needed". With a Racor filter and 3 1/2 gallons of 10w-30 I can do an oil change for less that 50 bucks, and change it out at 7,500 mi. intervals, with excellent UOA's.