Look at the list of runner-ups.....if they were all on drugs then how the hell did Armstrong beat them?
It would be a monumental achievement if he did it drug free!!
With regard to this year's Tour, times were down, and most noticeably in the mountains.
Read this article, it shows you how to spot a potential cheat based on power outputs. Interesting stuff and note that these outputs were being achieved this year whereas in the past they were exceeded.
For the record, I always had my doubts about the man
http://www.sportsscientists.com/2010/07/power-outputs-from-tour-de-france.html