Where have you been the last 30 years? The whole idea of Olympic athletes being amateur was abondoned in the 1970's or 80''s following accusations of "shamateurism".
Prior to that Athletes were allowed to receive expenses to help training but not to receive an income. A few were stripped of their medals when it was discovered they had been paid. Over time it became unmanageable and impossible to police so they gave up and threw the Olympics open to pros as well as amateurs.
Why pick on the Williams sisters as "the only pros"! What about Andy Murray, Roger Federer, Mladic, the entire British Cycle Team...
Pros from ALL countries play in tennis
Because the IOC scrapped their amateur rule a couple of decades ago, now anyone can compete if they're good enough.
The Williams sisters (Serena & Venus) are playing tennis and they are not amateurs but pros. That doesn't seem fair to the other people who are real amateurs. Does anyone know why this goes on?