Selecting the top 10% of those gets you 1700 students, which is quite close to the size of Harvard's acceptance statistic (of 2000)
The person you're replying to indicates that 10% is 1700, and that 10% may be more representative of the high-EC and 4.0 level.
I'm not sure a few thousand folks from around the country qualifies as 'bunches'. Thinking back to my high school days, we had only a handful of people who were both academically advanced and active in many EC - sports, music, theater, etc. Partially there's just not enough time in most people's days to get 'good' at multiple things, even if there's aptitude. Secondly, not everyone can actually afford to get involves in a lot of ECs (despite aptitude/talent).
I can't think of anyone I know from my school (class of over 600, IIRC) who was all 4.0 GPA who also did multiple EC work. We had people in both camps. And I had a pretty lousy GPA, but did much better on ACT than some of the high GPA kids.
I know someone who got into an MIT engineering program roughly around '03 and they claimed to have below a 500 on the old SAT verbal section (scored perfect 800 the math though).
Their claim was they purposefully did not study for the verbal section because 'excelling at rote memorization to get into the top schools in the world is idiotic at best,' something like that.