It's more likely it's because all of the H-1xx series firmwares are all very much the same, perhaps with a few very slight differences. It'd actually take more work and money to add the format option to the H-140 firmware and not include it in the H-100, H115 and H-120 series. Much easier just to work on a single piece of firmware than two different types
Plu sof course there's my other point; if someone wants to upgrade their microdrive, which will probably be eventually possible, they have the ability to format it with only the player.