The issue here seems the same for all the mentioned emulators, while he have developed a common lower layer graphic library for them, the actual emulation code is from other famous open-source emulators (original project or ports, all with non-commercial licenses). E.g. snesoid is based on a snes9x port.

Anyone with a G1 or G2/Magic will remember when all the yong's emulators suddenly appeared on the market nearly two years ago, at the same time he published nes/snes/gba/mame emulators. Considering the time needed to develop a single platform emulator that supports a good share of games (usually years, maybe with few exception in the history of console emulation), developing them all from scratch would have been impossible imho.