I may be wrong but I believe it makes sense that Skype sells music, if you look a little ahead of today. What is the future of the iPod? Answer: the "iPhone" What is the future of the cellphone? Answer : the "wifi-Phone" (by that I mean wireless communications made over Wi-Fi VoIP)
Skype is already Wi-Fi enabled on Pocket PC devices. If they start a music store, they will be at the cross between the iPhone and the wifi-Phone. I think it's a smart move.