I don't know but I'll hazard I guess that these problematic pages are departing from Sun's specification for Java, and instead are using some Microsoft-specific coding, and as such should be flamed.
Like the useless BT/Yahoo site which I'd simple have never visited if it hadn't been mandatory thanks to the idiotic 'upgrade' forced upon customers thanks to the 'merger' of Yahoo and BT's internet services, and the subsequent problems in accessing POP mail. (We've 'upgraded you to Webmail' - Thanks but NO THANKS you fµcking tossers . . . !)
Could you perhaps provide some links to the problematic sites?