Which resolutions the card can display once the drivers have loaded has nothing to do with VESA.
http://en.wikipedia.org/wiki/VESA_BIOS_ExtensionsChameleon reads available VESA modes directly from the video card BIOS. If your video card doesn't report 1900x1200 among its supported VESA modes, it won't be available for use as boot resolution.
Unless there really is a bug in Chameleon of course.
If you could prove that 1900x1200 is in fact a valid VESA mode for your video card I'm sure someone would follow up on it eventually.
There are tools for Windows that will allow you to extract and manipulate your video card BIOS which are normally used to alter clock- and fan speeds, but maybe you can see something about VESA resolutions too. Or maybe you could use a Linux live distribution with some VESA mode reporting utility or something (see link above).
It's up to you to deliver the evidence!
I get the "14MB video memory" too by the way, I don't think that has ever displayed correctly in any version of Chameleon that I've used (including pre-2.0) with my current video card. I don't think it's important, I doubt Chameleon itself is using anything close to 14MB video memory anyway.
I'm using my displays native resolution at boot, 1280x1024, which works fine. Your 1024x745 maximum does seem strange fwiw.
Have you checked if there's a BIOS update available for your video card?