The Kerbals are actually not as advanced as you think. They don't require food (ATM), its easier to get into orbit around Kerbin (I believe it takes more delta-v to get into orbit around Earth than to get to Jool in KSP), they are immune to radiation, aerodynamics are almost non-existent(ATM), and they have an unlimited budget(Once again, ATM). If real life was applied to KSP, it would be much harder to do anything in KSP, but that will never happen because KSP is designed to be fun.