Well, Tibet has been unique cultural centre centuries before Columbus has discovered America?

Yes, but many other areas have been, as well.  I have nothing against Tibet, and I'd love for its culture to be preserved, but these are people -- not Smithsonian artifacts.

The heritage doesn't disappear because of McDonald's and Levi's.  That's just "rubbish" (practicing my Britishisms ;-).  People don't have to buy Levi's jeans or McDonald's Big Macs.  I don't know why people shop with those two companies, anyway.  The latter is sewage on a bun, and the former is over-priced clothing that falls apart within a year.

Further, I don't understand why it's taken as a given that consumerism cannot be coupled with a maintenance of one's heritage.

Is it fair to ask that the people of Tibet maintain their traditional culture without giving them all of the available choices?

It's just as ridiculous as the claim that Wal-Mart is destroying "small-town America," which brings up images of the pretty, little Main Street stores and the local Methodist church and the harmonious community and all of that other bullshit.  (For me, it brings up images of anti-abortion protests, religious nutjobs, segregation, hunters shooting furry woodland creatures, and pseudo-patriotism.)  If people stopped shopping at Wal-Mart (or McDonald's or whatever other chain), it wouldn't be an issue.

If the traditional culture of Tibet is held to be so important among its people, it will remain important.  But people deserve to make their own choices.

Be nice to America. Or we'll bring democracy to your country.