Are pregnant women more susceptible to morning sickness?

Yes. Morning sickness is the lay term for the nausea of pregnancy. Hyperemesis is the medical term if this is significant. Basically only pregnanct women get "morning sickness".
Yes. Only pregnant women get morning sickness, but not all moms-to-be get sick. Your chances of feeling nauseated during pregnancy are higher if a) taking birth control pills made you nauseated, b) you get motion sickness, c) you get nauseated with migraines or d) lots of women in your family had bad morning sickness. Women carrying twins are also more likely to feel sick.