This is interesting as I just finished writing some code using Microchip's MpZBee stack on the PIC microcontroller. It's interesting to note that ZigBee is a closed standard (last time I checked). In reality, it's a set of improvements on the IEEE standard 802.15.4 which is specifically designed for low rate networks. I wonder what's the general view of ZigBee as a closed standard? Might that get in the way of it being adopted universally?

That makes absolutely no sense. HTML/AJAX interfaces are anything but consistent. Every application has its own interface. X is used to display a complete GUI on top of a system with respect to its hardware and configuration while HTML/AJAX depend only on a compatible browser and a javascript engine. It doesn't make any sense to compare X11 to HTML and AJAX, they're different things.