Are CD's and LP's mastered differently ?
Yes. Basically, it's easier to master for CD than vinyl format. Song sequencing, the length of each side, mono compatibility (stereo spread), deep bass levels and absolute volume are all should be treated differently when mastering for vinyl. Notice I say "should be". No harm is done by using the same master for each format, but the result clearly won't be optimized for vinyl.
That's a very good question. I've heard that early CDs were pressed from Master Tapes for vinyl resulting in bright sound. Is it true?