Actually, most refiners do add a few chemicals to aid stability, but they know almost all gasoline is used within 2-4 weeks of refining, so it is not cost effective to try for longer priods. And gas actually doesn't degrade much anyway in a closed tank. Chevron says up to about a year is OK in a closed tank at moderate temperatures (but not for two cycle fuel where oil is mixed in).
However, stored fuel can absorb moisture and stored diesel may grow an algae. So an algaecide is recommended for diesel if it is not being consumed regularly and "dry gas" additive is good for gas that sits in a damp climate.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL