AK: I believe Nikon has moved to a truly lossless compression as of the D3 generation ie. zero loss of data. At least that's true of camera categories such as the D700 that I own. I must admit I haven't checked the lower end models to see if lossless compression is available.
Maybe you're thinking of the very minute difference between 14 and 12 bit ADC?
But either way as has been mentioned, its all technicalities and pragmatically speaking there's really nothing worth worrying about.