AROS also has the advanatage that the PPC version could have a high degree of ABI compatibility with MOS and OS4 (look at the 0s4emu on MOS and the MOSemu on OS4)... this would allow purchacer of the AHT STB to run their OS4 and MOS software on a relativly cheap box, multi purpose box.
AROS also gives AHT "their own OS" bonus, allowign them to customise it to suit their needs, it's also quite a bit smaller than Linux.
