The main reason showing international game shows wouldn't work (Though it would be awesome) is primarily because, for example, Australian "WOF" is meant for... well.. Australians.
Another reason is foreign game shows use material local to the country.
Lets say GSN airs the South African version of "Millionaire". You might get questions like this:
"Who is the mayor of Johannesburg ?"
"TV Presenter Zanelle Roux hosts what popular show on SABC2 at 14:20 ?"
"In what year did Harold Maggs become a member of Parliament ?"
and "Shaun VanHelsing was born on 1976 in what province ?"
and you'd might see players struggle with "Who is the current Vice President of the United States ?"
Average Joe would go: "What the *DER BLEEPEN* is this ? I'm switchin' to Spike TV"
Also, the local culture. Some people would get upset by some of the customs other people do, and unaware people might mistake what they're watching is an American show, think those people are strange and then switch over to Spike TV.
And, the humor. People in other countries, no offense, are... lets just say, not as hesitant about making un-PC jokes/steryotypes as Americans are and some people might take serious offense at the "colorful" commentary.
-Joe R.