"The EIA232 standard is applicable to data rates of up to 20,000 bits per second (the usual upper limit is 19,200 baud). Fixed baud rates are not set by the EIA232 standard. However, the commonly used values are 300, 1200, 2400, 9600, and 19,200 baud. Other accepted values that are not often used are 110 (mechanical teletype machines), 600, and 4800 baud"

from http://www.camiresearch.com/Data_Com_...ndard.html

So what windows supports is what Microsoft allowed given the common hardware, not what is standard.

And by the way... LookRS232 has an upper limit of 115200.