This really isn't specific to Asperger's syndrome or the autism spectrum, and NTs actually probably fake emotions more. Here are some key terms from social psychology and sociology:
For example, you're going to the funeral of a friend's relative, but you never met this relative. You may be in a good mood that day, but when attending the funeral, you're expected to show a somber demeanor out of respect for the deceased's family and friends. You probably wouldn't be expected to show the level of grief of a spouse or child; in fact, bawling during the services would be inappropriate for you. Still, you probably shouldn't be cracking jokes or talking sports even if you're in a pleasant mood. Likewise, emotional regulation means that, if someone insults you or does something that annoys you, you can't let your anger make you punch them in the face.
I don't think NTs always show how they really feel; they go with the socially appropriate emotion most of the time whether they genuinely feel it or not.
On the other hand, psychopathic adults and children with conduct disorder with callous/unemotional traits are known to "sham emotions" and not really feel anything deeply. Specifically, psychopaths exhibit a general shallowness of affect, meaning a general lack of emotion spiked with brief, dramatic displays of emotion that seem intended for manipulative effect; psychopaths are also known to be glib and superficially charming, meaning they will use flattery and a superficial appearance of friendliness to get what they want. Psychopaths are also considered callous, lacking in empathy, unconcerned with the feelings of others, and specifically lacking in feelings of guilt or remorse when they harm others. Irritability is considered a diagnostic criterion of antisocial personality disorder. The psychopath's "deficient affective experience" is far beyond NTs' emotional work and any emotional/social difficulties people with Asperger's syndrome have, though.