No surprise. The G31/G33 series support OpenGL to v1.4 only. This does not even meet the desktop SketchUp’s minimum requirements.
See this Intel page under “Older Graphics Products”, 4th row in the table, for stats on the G33:
http://www.intel.com/content/www/us/en/support/graphics-drivers/000005524.html
Other Intel users can check the newer generation tables above this “Older Graphics Products” table.
In December of 2011, an Intel employee (named Diego) answers a question, in the Intel forums, by a G35 chipset user:
Currently only the drivers provided for newer platforms like the Intel® HD Graphics 2000 and 3000 are optimized to support WebGL.
So at this point, [2011] the latest drivers that have been provided for the Intel(R) 3 series chipset controllers, like the Intel(R) G35, are not validated to properly handle WebGL and there is no estimated time to know when a new driver will be released to implement support on this over older platforms like the Intel(R) 3 and 4 series controllers.
We can “read between the lines” that there is no money in it (so no impetus) for Intel to update any of the drivers for legacy products. They would rather that the desire for WebGL support drive endusers to buy newer machines from OEMs, which drives computer OEMs to buy newer chipsets from Intel.
So generally for Intel, end users need a 2nd Generation CPU / chipset minimum (with HD 2000/3000 graphics or better,) which supports OpenGL 3.1 minimum.
Looking at the Khronos WebGL 1.0 Specification:
WebGL™ is an immediate mode 3D rendering API designed for the web. It is derived from OpenGL® ES 2.0, and provides similar rendering functionality, but in an HTML context.
So, also looking for a card that says it supports OpenGL ES 2.0 (or better) wouldn’t hurt.