aPple has a long history against user maintenance. As long as I remember there has always been an 'ostracism' clause for doityourselfers. Adding a drive, memory or plain battery replacement have all been for aPple, cop outs to their warranty responsabilities.
Looking at it from their side, why make a car if you can't be the one to repair its gastank?
Personnally I would suggest to go with their service for a different reason. Even if it costs a few dollars more to replace that power cell than doing it yourself, you will be assured that this toxic object will be disposed of responsibly.