is cyber sex cheeting?

over the past 2 years I've been exchanging sex stories with different men via email. I never meet them, never give them my real name. Most of them are married and claim to have "sexless marrieges" and that writing me (and whoeverelse) is thier only sexual outlet. My question has 2 parts: 1) Is cyber sex - particularly in story form - cheeting? 2) Why do so many men claim to haev a sexless marriage but upon futher exploration, they reveal thet they do have sex with their wives, just not the way they'd like to...what's up with that?