"Pretty impressive, but for some reason they decided against using HTML5 canvas."
IIRC, it was because of browser incompatibilities. IE8 removed the VRML necessary for excanvas.js to work and yet doesn't have full canvas support, so they were in the odd situation where it worked on IE6, IE7, and standards-compliant browsers, but not on IE8. Googling, I've found that excanvas.js has since been updated to work on IE8, but maybe it didn't support the specific functionality they needed.
There're also pretty strict latency constraints on the homepage, so including excanvas.js and its canvas emulation is quite a few bytes that just aren't necessary if you use divs.
IIRC, it was because of browser incompatibilities. IE8 removed the VRML necessary for excanvas.js to work and yet doesn't have full canvas support, so they were in the odd situation where it worked on IE6, IE7, and standards-compliant browsers, but not on IE8. Googling, I've found that excanvas.js has since been updated to work on IE8, but maybe it didn't support the specific functionality they needed.
There're also pretty strict latency constraints on the homepage, so including excanvas.js and its canvas emulation is quite a few bytes that just aren't necessary if you use divs.