A good statement... Yeah, it's Keirsey. For sole believers of Keirsey, it's cool to write an article like that.
Yet still, there are really not many traits, definitely not 23, that all the MBTI types of introverts commonly share. It's very hard to state things like "introverts spend more time on the computer", when plenty of extroverts spend even more time on the computer, but for communicating with people, playing online games or extroverted-sensing-oriented games like Call of Duty, Crysis, Battlefield etc. instead.
There is no "typical non-descript introvert/extrovert" stereotype, just as you can't describe "that dude never cleans up after himself" as perceiver and "That girl works as a
masseuse" as sensor, and you can't tell someone being a thinker solely because they're good at math, because obviously all feelers suck at math etc. etc. etc.
Describing people, using psychological terms to assign non-descript stereotypes is definitely not very helpful. From the viewpoint of cognitive functions MBTI, dividing people as introverts or extroverts is exactly like that.
That is almost as saying "All canadians are very generous, and americans are living up to american dream, thus very happy with their lives." It's misleading and certainly not giving any useful information, as very large groups of people that only have the environment in common cannot possess the same non-descript personality, unless the group is lead by Hitler. Dividing introverts and extroverts in more categories is something that avoids misleading people, giving them actually interesting read that does not (in)voluntarily lead them to believe that the stereotypical introvert is INTJ and stereotypical extrovert is ESFP.
Do you mean Keirsey's theory? Cognitive I/E and common conceptions of I/E need not be universes apart, even if they may not always be the same.
Just because someone does not relate to any of the 23 introverted traits doesn't make them loud and obnoxious, and relating to all 23 does not make a quiet loner.