When you're dealing with a state that has the economic clout that China has, and the kinds of hyper-reactive sensitivities that China has about Tibet [1], you tend to defer for sake of a smoothly functioning global economy, whether you agree with their position or not.
[1] For example, barring people from getting a Chinese visa for life for publicly making pro-Tibet statements.
Another: you need an "internal" visa, issued from within China, to get into Tibet [2]. If you mention on your visa application to get into China in the first place, however, that you want to visit Tibet, your Chinese visa is automatically denied. Essentially, you have to lie to the state about the purpose of your trip, if you want to visit Tibet. No, they don't have any issues there at all...
[2] Unless you're flying into Lhasa from Kathmandu, where you can get a direct-entry visa.
[1] For example, barring people from getting a Chinese visa for life for publicly making pro-Tibet statements.
Another: you need an "internal" visa, issued from within China, to get into Tibet [2]. If you mention on your visa application to get into China in the first place, however, that you want to visit Tibet, your Chinese visa is automatically denied. Essentially, you have to lie to the state about the purpose of your trip, if you want to visit Tibet. No, they don't have any issues there at all...
[2] Unless you're flying into Lhasa from Kathmandu, where you can get a direct-entry visa.
EDIT: footnotes.