I'm just going to take this opportunity to shake my fist at Internet Explorer, because much of this stuff is useless on production websites (some things are usable with Javascript hacks).
<input type="text" x-webkit-speech>
var a = new ActiveXObject("SAPI.SpVoice");
And don't forget MIDI and Drect3D support was introduced in IE4. Before SVG, there was a trend of VRML in the industry and VML was added to IE.
And don't forget, the very first AJAX as made possible by the IE xmlhttp object.
TIME+dHTML was cool before Flash, even before these Web2.0 and HTML5 cool kids start yammering around.
And then Microsoft killed these features with their Silverlight.
Also, if webkit has settings or features that are specific to the library used, it makes sense to put those in a different namespace as well, to avoid pollution.
MSXML XMLHTTP. MSXML 2.0 released with IE5 was first to support it. It got copied first by Mozilla, BTW, then as AJAX caught on in 2004 Safari copied it too.