The difference that they are selling is that it is Cas 4 ram[4-4-4-12 as opposed to 5-5-5-15] for the macbook and macbook pro's, but also they mention that these chips "features special Serial Presence Detect (SPD) profile characteristics, so that Macs can self-configure for optimal performance for critical applications."
I know it is not out of the realm of possibility for a tech company to float some bogus # or performance enhancements that don't actually do much of anything but I wouldn''t expect this from Crucial.
Maybe I give them too much credit, but here is one thing to consider...
I have seen windows users(the non-bootcamp variety) post that they have put CL4 chips in thier systems and noted CPU-Z reporting the CL4 being recognized.
Perhaps this is possible in the santa rosa Macbook/MBP platform? [Merom&Penryn]
As far as I know(and I could be very wrong), I have never seen a definitive answer from anyone stating that the EFI on the macbook/MBP lines cannot detect CL4 ram as CL4, usually people just saying that it probably doesn't or most likely wouldn't...