When you are traveling on a budget holiday rather than business - time is not so important. rkkwan is certainly closer to the area than I. And I respect his knowlege.
But my approach to travel and accomodation is very different from the normal FT poster.. Lonely Planet versus the Michelin guide I suspect. As well as country versus city.
A bit of research suggests that the bus ride from the airport in Lanzhou is still 30 RMB. And probably after a long(ish) wait. However, there were a number of local men on the bus happy to talk about their city, where we were from and where we were going (in English). In the end the approx hour ride (once started) seemd to be rather less. And of course this perception would have been affected by the excitement of our small group being in "local" China for the first time. My point was (is) that there is an acceptable alternative to the taxi (and its costs). My apologies if I was unable to convey that.
In Lhasa yes route to the airport has a major detour to cross the river. There seemed to be construction of a highway bridge which would have shortened the route - though I can find no current references to it on the web. Perhaps again the time perception was altered due to going somewhere to/from other than the airport. Given the altitude, I would not fly into Lhasa if there were any other alternative I could fit into my time schedule. Most of the tour packages I see advertised include the transfer(s). We were traveling independently but arrived from Golmud by b*s. Now I would use the train - though probably not the "tourist special". Both avoid the airport but have other issues - mainly the extra time.
In any case I hope that the air in Lhasa is never as polluted as that which we found in Lanzhou.....
Happy wandering
Fred