Well, piratePenguin, I hope I never hear you bitching about IE crashing "for no reason" then.
There's a good reason why document.write doesn't work for xhtml, it'd potentially corrupt the document and that just can't be allowed. XML has to be verifiable, and if it can be fucked up during runtime by incompetent webdesigner, it's a bad thing. My friend didn't think of this, as he was trying to write xml table renderer that could sort by any column. Well, you can use xsl to sort stuff, but you can't use xsl to rewrite the page after it's been translated once. I recall he ended up writing a html page with javascript to do the XSLT and rewriting the html page instead. Either way, he seriously tried to write javascript into XSL, and learned it isn't supported. The surprise was that firefox crashes when this unsupported operation is tried.
Anyway, a crash bug is critical, always. It can be exploited to annoy the user to no end, and I'm sure you'd bitch about microsoft if we were discussing an IE crash bug that hasn't been patched for two years.