RMC has the Whip listed because the old RM2 has it like that.
Personally, I think that the whip is a slashing weapon, not a crushing weapon, so I would go with RMX's handling of it.
In the upcoming Combat Companion, the Whip is actually in its own weapon group (the RMC/X 5 weapons groups get trashed in the Combat Companion, and instead there are about 26 or so weapon groups, but only a couple sets of costs - Express Additions #4 gives you something of a small preview of this... (Note: the CC rules have changed slightly, so the costs from EA4 may not match those found in CC)