I think .com is top because humans are creatures of habit. .com was the first so everyone knows / is programed to type .com.
When the current generation grows up seeing multiple extensions as a norm that's when .com will lose it's luster a bit.
I asked this question before with no replies so I'll ask it again.
Where do you guys think the internet will be in 20 years?
Lets look back 20 years.
http://www.computerhope.com/history/1993.htm
Now take into account that the web is used by way more people now but by only a fraction of the population. So with population growth and increased social use where will the demands be?
These new Gtdl's are throwing a curve ball over the plate, that's for sure.
Just my 0.02$