Well, the simple solution is to ban all the riders who actually do well, that way I think I may get a look in on the Tour next year.
The history of cycling is not a great one, however, the assertion that anyone who does well MUST be cheating is rather strong.
Does that apply to Olympic cyclists? Our womens pursuit team, must be on drugs. Sir Chris Hoy, yeah, him too. Laura Trott, Victoria Pendleton, clearly all doping. And while we're at it, Usain Bolt did rather well at the Olympics too, I wonder.
At the end of the day, you cannot accuse people of cheating, just because they do very well at something, otherwise, there is little point in ever trying.
Technology has moved on, understanding of the physical demands on a rider, and the training requirements to improve these, along with analysis tools and so many other aspects, the electronic shifting alone has to be worth a few seconds, Aerodynamic frames are equivalent to an increase in power of 22 watts (against an average of 375 ish on a climb) add weight reductions and stiffness improvements brought about by improvements in frame technology, and this all adds up.
An interesting article:
http://www.guardian.co.uk/sport/blog/2012/jul/10/tour-mountains-science-of-sport
And TDF times and speeds for comparison:
http://bikeraceinfo.com/tdf/tdfstats.html