The male avatar at left is upwards of 7 feet tall, which is actually a typical height for SL avatars. Linden Lab's avatar adjustment sliders allow users to set their size to over 8 feet, which inevitably drives the average height upward. (Because how embarrassing is it if your avatar seems short compared to others?) That's led to a world where the female avatar on the right, who is 5'7" (which in real life is actually on the tall side for women, on average) seems dwarfish. The problem, veteran Second Life content creator Penny Patton explains in this long, detailed, and persuasive post on the official forum, has hurt the quality of Second Life building as well. (Imagine if real life architects designed homes assuming all their customers were in the NBA.)
As Penny puts it to me, "SL content creators can craft a richer, larger and more detailed world in Second Life, simply by building smaller -- but Linden Lab has to help them by encouraging most avatars to shrink down to a much more realistic size." Read her case here -- you too, Lindens reading this! While you're at it, I'll add an idea to the mix: Monetize avatar height, so that anyone who wants an avatar over 6'4" has to pay extra for that privilege. This would drive average heights down to a more reasonable proportion, while still giving the gargantuanly-inclined the freedom to do so.