in the ep. riechenback (hope i spelled that right!) fall,as the reporters say each sentence,one of them says james moriarty instead of jim......so was that a mistake or like,done in purpose?

You obviously watched very closely. :D It's probably because "Jim" is short for "James".

Jim is a nickname for James and they were being formal

it was no mistake jim is a nickname

On the news they usually say full names because it is a formal news source and the investigations that they depend on for their news is proper and refers to people as (in this case) James instead of Jim. Jim is just a nickname or a shortening for the name James

Jim is just a nickname for James. It's actually spelled Reichenbach Fall (Something that helps me when I'm spelling German words is that if there is an 'e' and an 'i' together, you pronounce the second one. That's why e is before i in Reichenbach)