While looking at the time conversion methods in .NET, I was surprised by this entry in the .NET Date and Time FAQ:
Q: “Does the .NET Framework support time zone conversions to any given time zone?”
A: “People are often surprised why this feature cannot be supplied by Microsoft at low cost. In particular, data to do conversions exists in the Windows registry and is used by the time zone selection dialog. However, there is a big distinction between having UI and registry data and having an API. This is a more expensive feature for Microsoft to undertake than most people would imagine because (a) an API must provide consistent behavior from one machine to another so we cant just re-expose the registry data, and, (b) there is cost for Microsoft in exposing an official time zone conversion because we face ongoing geopolitical costs for any country/region based data we gather and maintain. For example, a country may threaten to boycott our product if it is not listed in the data. This has happened to us with our CultureInfo data on many occasions, and we often need to tweak data in service packs, which is expensive and risky.”