Roleplayers are just that, people playing a role. They think they are something like a vampire, werewolf, mermaid, etc. and try to convince others that they are becaues they believe it so truely themselves. Much of this is due to the media(eg movies like twilight, tv shows like buffy, angel and charmed, the list goes on), also some come from games like WoW, D&D, and such.
You'll find many a thread on here quite against RPers, mostly because they can't seem to understand this isn't an RP site and is instead for REAL magick.