This question comes up with a great number of Apple machines, especially those with soldered memory. In short, Apple tests and guarantees the machines to work with the highest capacity of memory that is readily available at the time that the machine is produced. 2GB memory sticks, either SDIMMs or SODIMMs, are not readily available, as there are few companies making them, and even they produce far fewer of them than 1GBs. As such, Apple didn't test them. Likewise, when the original 12" PowerBook was released, 1GB SODIMMs were not readily available, despite the fact that they will work.
As for the suggestion that the software limits the recognized ram, this is false. Since the advent of OS X, there has not been any significant limitation on recognized ram. The OS is built to recognize more ram than you could possibly stuff into a current machine. OS 9, however, only recognized up to 1.5GB os ram total.
Essentially, if you want to spend the money on the module, it's likely that it's going to work. However, Apple will not support it officially. This isn't to say it will void the warranty, but according to Apple's official line, "It won't work". From a technical standpoint, there seems little reason why it would not work.