Robert O’Callahan: It seems clear that for now we have no market need for drastic multi-engine compatibility, and therefore there’s no need to even consider the pain it would cause.
Apparently, the clear difference between Mozilla and IE is in the expectations that they set. Jeremy Keith analyzes what it could mean for IE users and IE itself. Hopefully the public beta for IE8 allows time for refreshes based on feedback, and is not merely an exercise in populating the README.
A related thought: Chris Wilson once said: I made the decision to not try to support the MIME type in IE7 simply because I personally want XHTML to be successful in the long run. Either IE8 will continue to not support XHTML (disappointing literally dozens of people), will implement a different default for
X-UA-Compatible, or be in the rather odd position of effectively requiring either the HTTP header or meta tag in order to function at all.