Lance wouldn't have had to work. His teamates, as well as probably all of the other teams would have done the work to chase him down right away. Dont you remember how high the pace got later on in the stage?
Tradition dictates that the last stage of the tour is a celebration, unless it is a time trial. The first half of the day is not even really a race, its pretty much a rolling party, cigars, champagne, hookers, blow.
The yellow, green and mountain jerseys ride along together to provide good photos for the press, Lance wears a womens wig, Jalabert puts on propellor hat etc..
As they get closer to Paris, the attacks start, but believe me that the Posties know where Ullrich is all the time. If Bianchi did decide to try and get away and team time trial it to the finish, They would be caught. Sure Postal would chase, but so would all the teams with the good sprinters. The green jersey battle came down to the last day remember?
It's the last chance for a stage win, and stage wins do more than make sponsors happy, they also help you get a better contract the following year. Plus it's great bragging rights to win on the Champ Elysees.
The french teams would definatley chase too, as they did not have a particularly good tour, and were desperate for good performances. A Frenchman did win that last stage, Jean Patrick Nazon winning for the Jean Delatour team.
If Ullrich and company had attacked, the French press probably would have frowned on it. Ullrich had plenty of time to beat Lance throught the race, he just couldn't do it when it mattered most.
Now if I could just find that picture of Jalabert......
Well I guess if you're going to win a grand tour, you deserve to celebrate
Its no fun though if your rival goes out on the attack while you're back at the team car finishing off a line. Ullrich understands that and races with respect.