I'd be interested to find out on what basis (in terms of solid proof) Hamilton was making that claim, because even with the laissez-faire attitude to doping that seems to have permeated the sport (right from the UCI on down), I doubt many people were running around the hotels with needles in their veins or nipping to the next door bus to borrow a phial of EPO.
Just to put the 80% figure into perspective, in the TdF peloton Hamilton would have had to observe 149 other riders (22 teams of 9 minus US Postal's 9, because he already knew about them) doping - unlikely to say the least!
Hamilton is entitled to his opinion, but the figure given smacks of an attempt to justify his actions (and by extension those of Lance Armstrong).
Hamilton also fails to define "doping" - I'd categorise the use of a cortizone cream (for example) in a lower category of "doping" than microdosing EPO.
For his figure of 80% to be correct he'd have to be amalgamating all the "categories" of doping into one, and therefore attempting to smear the cortizone cream user with the same brush that has been used to tar him.