Robert Feder addresses this in his column this morning. It makes sense for CBS to move them there. The Score is losing the White Sox (to WLS), so they now have the airtime available. On an all-sports station the Cubs can get the full coverage they deserve, which I really felt was lacking on big game days at WBBM. (Not the station's fault--it wasn't their format).
On the other hand, the Score lineup is very Sox-fan-heavy. I've always thought it didn't represent the actual market in that regard, but figured they were the White Sox station, so no harm, no foul. If they become the Cubs station, they're gonna have to swallow that a bit. I think they've been pretty good about softening the temple-throbbing black-hearted hate this year (Sox fans in general), so maybe it won't be an issue.