oldsaw
"Been There, Milled That"
My Dolmar 7900 manual states:
Dolmar Oil 50:1
Other Oil 40:1
I think it is just the manufacturer protecting themselves. They know the quality of their own oil but who knows if a consumer would try to use some 30 year old Homelite oil that isn't of the same quality.
I run Stihl Ultra 40:1 in all my saws.
It creates a false economy with their oil. You mentally discount 20% if you know math and aren't thinking it through.
There are standards.
Mark