Looking at one of the proven dirtier races in 2011, the women's 800m, the Russians accounted for 37.5% of the final:
1st Caster Semenya South Africa 1:56.35
2nd Janeth Jepkosgei Kenya 1:57.42
3rd Alysia Montaño. United States 1:57.48
4th Maggie Vessey United States 1:58.50
5th Kenia Sinclair Jamaica 1:58.66
DSQ Ekaterina Kostetskaya Russia 1:57.82 DSQ Yuliya Rusanova Russia 1:59.74
DSQ Mariya Savinova Russia 1:55.87
If we assume the other runners are clean this roughly fits in with the statistic quoted (circa 30%).
However, there were only 2 male Russians in total in events from 100m - 10,000m (incl. steeple & hurdles).
This suggests that there must be a large number of dopers from other countries such as Ethiopia, Jamaica, Kenya etc. (possibly even USA but less likely IMO).
I just wish his Lordship (Coe) could actually deliver on his anti-doping rhetoric.