Writing by th book

Why is it that people who are in the begining stages of playing alway say " You dont have to write music by the book" What book are they talking about. There are general "rules" to writing good music, well music most westerners will pay attention to. For example... Transition.. You need to ave a good flow of verse-transition-chorus0-verse... blah blah.. a song has to have structure.. in some form or another otherwise the sound and motion of the music go's nowhere... In past bands this has been a consistant issue. If I say anything reguarding "theory" all i ever get is "by the book man" anyone else have similar problems with people? I hate to be a dick and say, " I wont play with you unless you know what your talking about" Cause everyone who play's is in one stage or another in learning... I dont know... I guess this was only a bitch session lol let me know what you think on the subject.