Well, let's have a look:
2007 Denis Menchov (Rus)
2006 Alexander Vinokourov (Kaz) known doper
2005 Roberto Heras (Spa) subsequently the title was stripped from him and went to Menchov
2004 Roberto Heras (Spa) known doper
2003 Roberto Heras (Spa) known doper
2002 Aitor Gonzalez (Spa) known doper
2001 Angel Casero (Spa)
2000 Roberto Heras (Spa) known doper
1999 Jan Ullrich (Ger) known doper
So that's 7/9 For the Vuelta.
The TdF doesn't get much better.
2007 Alberto Contador (Spa)
2006 Floyd Landis (USA) known doper
2005 LA (USA) By now, who does he think he's kidding?
2004 LA (USA) Various
2003 LA (USA) Positive
2002 LA (USA) Tests
2001 LA (USA) All been covered up
2000 LA (USA)
1999 LA (USA)
1998 Marco Pantani (Ita) known doper
1997 Jan Ullrlich (Ger) known doper
1996 Bjarne Riis (Den) known and confessed doper (a rarity ey?)
So, potentially 11/12 for the TdF, 12/12 if the puerto alegations can be made to stick on Contador.
Giro fairs slightly better
2007 Di Luca (Ita) known doper
2006 Ivan Basso (Ita) known doper
2005 Paolo Savoldelli (Ita)
2004 Damiano Cunego (Ita)
2003 Gilberto Simoni (Ita)
2002 Paolo Savoldelli (Ita)
2001 Gilberto Simon (Ita)
2000 Stefano Garzelli (Ita) known doper (masking agent, 2002 Giro)
1999 Ivan Gotti (Ita)
1998 Marco Pantani (Ita) known doper
1997 Ivan Gotti (Ita)
4/11 isn't so bad by cyclings standards, but for any other sport there would be a massive scandal. Guess that shows how low cycling has sunk. Total dope rate is 25/32. Damn that's bad.
Still, some people do seem to have recognised this, and we can only hope for a better future.