Not true, the base oil breaks down and looses it's viscosity and it's ability to lubricate properly. This is from the Amsoil website:
Viscosity loss – A lubricant’s viscosity is its most important property. Viscosity has a direct bearing on wear protection, and your engine is designed to operate best using a motor oil of a specific viscosity (e.g. 5W-30). The intense pressure the oil bears as it’s squeezed between moving parts, like the piston ring/cylinder wall interface, can tear apart, or shear, its molecular structure, leading to viscosity loss. Suddenly, the 5W-30 motor oil your engine was designed to use is now essentially a 5W-20 oil, and wear protection may be compromised.
Here is more about the base oil from their website:
Though all motor oils eventually deteriorate, synthetic oils last longer than conventional oils and deliver improved protection against wear and deposits. They’re formulated with base oils that are more resilient to oxidation and heat, while their additives also typically offer improved performance.
Oxidation – The interaction between oxygen molecules and motor oil molecules naturally leads to chemical breakdown. Just as oxygen causes a cut apple to brown or exposed metal to rust, it breaks down base oils and reduces motor oil’s effectiveness. Oxidation can lead to increased oil viscosity, which negatively affects energy efficiency. It also causes the formation of harmful deposits and sludge.
High heat – Today’s engines run hotter than ever before, with temperatures up to 235°F, and even higher if towing or hauling. The rate of oxidation for oil doubles for every 18°F increase in temperature.