1) Usually when people say they like Rock, they aren't talking about Rock n Roll.
In the beginning there was Rock n Roll. Many of Elvis' songs are in this catergory. So are many of Beatles' songs of the early 60s.
Rock n Roll later evolved into many different forms: Hard Rock, Soft Rock, Alternative Rock, Punk Rock, etc. Nowadays the term Rock is used to refer to the entire family, including Rock n Roll.
Rock n Roll is the earliest form of Rock, when the term Rock didn't even exist yet. It has its own distinct and unique beat and rhythm, which is different from the rest of Rock.
The Rock most people talk about and listen to nowadays belongs to the post Rock n Roll era. It's Rock but not Rock n Roll.
Personally I like Rock n Roll more than any other kind of Rock.