Tja, mitt svar over gir bra forklaring, mener jeg.
Utsnitt fra din link hos Wikipedia, om syntetisk olje:
Their specially designed properties allow a wider temperature range at higher and lower temperatures and often include a lower pour point. With their improved viscosity index, true synthetic oils need little or no viscosity index improvers, which are the oil components most vulnerable to thermal and mechanical degradation as the oil ages, and thus they do not degrade as quickly as traditional motor oils.