Because, according to mediacodespeededit, the H20L firmware (which would be about the same as the H20/22N) supports a hella more media than the H10A/N, including way more DVDs +/- R DL and more DVDs +/- RW.
Absolutely not. The H10x series of writers uses an entirely different chipset from the H20x (and apparently the H22N) as well. The H10x series of writer uses a Renesas chipset while the H20x (and it seems, also the H22N) uses a Panasonic chipset. You’ll kill your drive if you try and use the wrong firmware on the wrong drive.