A good point in general. Although in this case this was a specifc question from an FTer whose profile snapshot at the left of the original post clearly shows they're in the US, and furthermore I know SAPMAN from, among other places, the Southwest Airlines forum (Southwest being an airline that flies within the US only and that doesn't partner with any airlines outside the US so far).

Which is why my answer in this case was automatically based on Diners Club US.

Btw, the mention should of the country in place of (or in addition to) the issuer. The issuer alone doesn't clarify much. For example, even though Citi is the issuer in several countries, the costs, benefits, point earning and redemption ratios, etc, still vary widely even among the Diners Club cards Citi issues in those different countries.