Are you saying that Robert De Niro's level of Introversion is representative?
It is representative of the introverts i'm accustomed to. Perhaps my view is skewed by more intense introversion? My understanding is that introversion is more than just being a little shy and spending some free time alone, but rather it is someone whose energy is depleted by the pressures of social interaction whether this be performance, small talk, interviews, etc. While it is true that people often choose to do what they fear the most, the introvert's recovery time will be apparent in their life. Here are some examples of introverts including some performers.
1. Principal performer for a major orchestra in Chicago spends her off season living completely alone in a remote cabin.
2. University composition professor lives alone and resists the efforts of neighbors to interact. He doesn't greet those he passes or engage in small talk. He is seen as aloof and austere. He spends his time alone composing, reading literature and philosophy.
3. Programmer with social anxiety lives alone and only interacts with others online. He works from home and occassionally drives to a scenic location to spend time taking pictures which he then posts on the internet. Days, even weeks can pass without interacting with people irl.
4. An introverted couple never once in their lifetimes have anyone over for dinner. They spend much of their time together on their computers or watching tv. They rarely ever interact socially outside the home.
5. A fledgling performer gives a few concerts a year which are dreaded for their social dimension. While setting up the eager audiences watch her asking questions. This creates a level of anxiety and depletion that places the performance at risk.
6. After attending a required society meeting in which there are politics and social complexities, one introvert spends time observing and smiling, then immediately falls asleep on returning home in order to recuperate.
7. An introverted programmer is distracted and uncomfortable with questions about his life and thoughts. He feels no pressure whatsoever to answer. He is unbothered by the potential social tension this creates.
Everyone feels a little shy in life and can get tired from too much activity. Introverts are a minority because they require alone time primarily to recoup. Most people are somewhere inbetween where they can get some energy from people and some from alone time. Introverts who spend their entire lives performing, giving interviews, meeting fans, etc. would either go crazy, require stimulants, or significant alone time that would be difficult to miss. The celebrity lifestyle pushes the boundaries of what an extrovert can handle. It is not the domain of the introvert. The context really skews things. We see someone nervous or reticent in a highly social environment and assume introversion. Extroverts get nervous over this stuff. Introverts tend to shut down in relation to such environments. DeNiro showed signs of shutting down. The rest don't. I was also going to suggest that Kidman is not an introvert after thinking about it more.