In this case my numbers, greatly hedged by simply claiming a majority, came from directly measuring many millions of visitors to Wikipedia.
It is true that Java penetration is in decline but it still ships as a standard pre-installed component on many systems and it is still is required for access to many business web applications. While the geekerati still hate Java, as they always have, Joe sixpack simply doesn't care. For all the same reasons that he has Flash he has Java. (and, in any case, Theora in Flash 10 VM appears completely possible if anyone cares to do it Vorbis is already done)