Well, I know you've gotten alot of responses already, but I'll add mine anyway. The only difference a CD or DVD makes is if your computer has a DVD drive. DVDs have alot more space and the files are very large, so if we burn a wedding, it would be at least 2 CDs, so we usually burn it to a DVD since most computers these days have DVD drives. DVDs and CDs may be obsolete in the future, so it is good to keep a copy of allyour pictures on an external hard drive as well.
Photographers are usually instructed (at schools and conventions) not to give up the copyright. Traditionally it was never handed over. In this digital age, however, it is becoming in higher demand and photographers who will sell the copyright get much more business. When we got married, we didn't have a CD or anything but we did purchase it after a few years. Sometimes you can get the high-res images a year or so later for a more reasonable price if it wasn't included initially.
One other thing to consider with photographers is to have 2 shooters. It is amazing how many things are going on, and how much more of your day is captured with 2 photographers. It is also great because then you have 2 perspectives capturing with their artistic eyes!
Hope this helps! Let me know if you have other questions!
Katie