I doubt that VB6 is actually the only justification for COM's apartment threading model. If that were the case, then I don't think WinRT would still have ASTA (

I doubt that VB6 is actually the only justification for COM's apartment threading model. If that were the case, then I don't think WinRT would still have ASTA (application single-threaded apartments). I think the real rationale is that making sure certain code runs on the UI thread is something that applications have to do all the time, even today, even on non-Windows platforms.