I understand that the longest day is 142 miles roughly during one of the stages. Is this pretty much the same year to year as far as mileages of each stage or do they differ?

it does vary, and you used to see TDF's with at least one stage approaching 200 miles. Recent trend has been for a little shorter stages. Stated reasons: 1) to make the racing more exciting (too long a stage can make for slow dull racing) 2) to make it more humane. (after the Festina drug crisis, thought that too hard of a race pressures riders to use banned substaances, 3) prssure from the riders (although I don't think the TDF organizers worry too much about the rider's feelings).

4 of the 10 shortest tours ever are since 2000. When you realize that the 3 shortest ever were 1903-1905 and for '03 and '04 there were only 6 stages resulting of an average stage length of just over 404 kms. '05 haf 11 stages. For a long spell the tour was in hte area of 5400-5700 kms. Now it is 3400-3500.

So yea it has gotten shorter, both in total and per stage.