All digital cameras have firmwares. Firmwares are programs 'hardcoded' for specific electronics. As you are referring to a200, there is no update to the factory firmware.
My only explanation is that when a100 was released, it was the only camera Sony had, thus has additional features such as MLU then. Now, this feature can only be found in a700 which comes out about the same time as a200,a300,a350. These cameras varies in features and of course price. It is probably a Sony marketing approach than a functional problem.
The A100 was an update to the Minolta 5D. It's quite a feature-packed cam. You should trat the A200, 300, 350, 700 and 900 as a whole different series. The A200 is not really an upgrade to the A100.
It was also Sony's first DSLR, and came out before the whole craze for budget DSLRs really kicked off. At the time it was competing with the D70 and the Canon 400D, and was similar/cheaper in price.