I don't really understand why it is necessary? Cannot they just take top 100 sites from a rating like Alexa? And if they want to evaluate the performace, they c

I don't really understand why it is necessary? Cannot they just take top 100 sites from a rating like Alexa? And if they want to evaluate the performace, they could buy a cheap Celeron or Atom-based laptop with Windows and browse those top 100 sites. I am sure that this will give more information than any statistics.