re: Alexa and large sites, sometimes it's more accurate than others and one of my personal sites was pushing over 1M visitors a month once and they ranked it reasonably well at the time being well above 20K in their ranks but traffic volume has nothing to do with the number of people running the site.
Look at PlentyofFish, the guy was also a one man show that tossed up a UGC free dating site which went ballistic and he made a small fortune on AdSense so traffic volume and earnings has nothing to do with the size of the team and everything to do with working smart and not working hard.
One person, one database, one really fast dual quad core CPU server with lots of RAM and and lots of cache and a kick butt idea and you can easily handle tons of traffic and make make buttloads of money but you really have to get it right to be that kind of a success.
A little luck doesn't hurt either.
The problem IMO is that now the spotlight is on their site a bunch of people will try to try to directly compete with them instead of learning from them and applying it to other areas being neglected in the AdSense ecosystem which is the real pitfall of being held up as an example for the rest of us to learn from.