Oil continues to improve. Now there are micro filtration systems. Additives can be added back into the oil to prolong its life.
A diesel tractor ran one million miles on the same oil using the above methods. The carbon chains in synthetic oil do not break apart like regular dino oil. The dirt in synthetic oil can be filtered out by adding another filtration system. Additives are no big deal to put back in.
I am a big fan of synthetic oil. It makes for easier starting in the winter, it last longer, and it is really good for vehicles that do not get driven much.