I think that humans are taller than we were millions of years ago. So yes, in some sense short people are getting selected out. (Though I don't have data. I'm actually more confident that we're taller than we were thousands of years ago, than that we're taller we were pre-agriculture.)
2.5% of people will always be 2σ below the norm.
Curiously, sexual dimorphism may have something to do with our mating habits
The sexes differ more in human beings than in monogamous mammals,
but much less than in extremely polygamous mammals.
http://en.wikipedia.org/wiki/Sexual_dimorphismI don't follow. If a trait is sexually advantageous, that doesn't mean the trait won't be normally distributed at any given time. It just means the trait will tend to increase with time. And I claim that this does in fact happen with height.
I also predict that if you did cross-cultural studies, you would find: in almost every culture, when people are free to choose their mates, taller males have more dating/marriage success, on average, than shorter males.
Of course you don't have to be the tallest and the strongest, but it helps.
http://www.scientificamerican.com/article.cfm?id=why-are-we-...