So I decided dig into some real statistics. For stage length, I relied on the excellent web site Memoire du Cyclisme. I found these pages easier to mine than Wikipedia. So I wrote a Perl script to download the relevant annual web pages from the site and sweep the HTML for stage lengths.
First, I plot the data for each year using a log-normal plot. The x-axis describes stage length, while the y-axis describes the rank of the stage having that length. Each decade in the plot (only even decades to avoid too much clutter) is then represented by a curve. The median stage has a y-value of zero. So if stages in a given year are longer, the curve for that decade will be further right. I added the plot for this year's Tour as points.
You can see a clear trend leftward. Stages have been getting shorter. But while the long stage this year may be relatively short, the points for 2010 fall generally on the curve for the previous decade (2000-2009).
There's a lot of information in that ranked distance plot: maybe too much. To simplify, I extracted the median stage for each decade, along with the average maximum distance for each decade. Again the trend is clear. The median stage length has been dropping. But more dramatically the truly monster stages from decades past has been diminishing.
A lot of this probably has to do with the changing nature of the Tour. The Tour started to sell newspapers. In news stories, you can't see speed, it's hard to grasp speed with words alone. But distance: that's another matter. Reading of epic journeys as riders travel more than 400 km in a day, starting not long after midnight and finishing just in time for the paper's deadline, is inspiring. People wanted to read each day not only of who won, but more importantly who'd survived.
These days, it's all about television coverage, and television only has so many hours. Make the stages too long, and riders slow down, finish times become less predictable, and the Tour becomes logistically more expensive. So while fans still demand the organizers expose the riders to an adequate amount of suffering, the days of stages over 250 km seem to be over. Want a death march? Check out Race Across America. The Tour is about speed.
So what next? Will the trend continue? Or will the Tour hold firm at its current length. I may be old fashioned, but I like the long stages. The average rider can, with a bit of training, do 200 km in a day. Certainly it makes the Tour more inspiring if the pros do at least a similar distance. It makes the race epic in a way it wouldn't be were the stages more comparable to a typical US race.