It seems to me that the CDR was added primarily as a way of transferring data to and from the internal hard disk. Once the decision was made to include the CDR drive, then someone must have given some thought of what else could be done with it. While many of the advances in the Genesys are geared toward quality and convenience, the vocal removal aspect appears more geared toward home entertainment. This is just a fun feature that GEM added because they could without too much expense. It does not have to be perfect to be fun. If it were perfect, it would still have little commercial use due to copyright restrictions.
As something that could be added for more fun at little cost, I think the karaoke features are a plus.

Arranger enthusiasts are familiar with the weird mentality that adding a feature somehow diminished the value of an instrument. I think if Korg or Kurzweil added arranger features (which could be turned off) to their Triton or K2600, respectively, they would sell less well. However, I think this reflects badly on the customer base. In this case, GEM has included karaoke features in a keyboard--so does that make it better or worse?