see understand this way.
Webpages reside on your webserver.
webserver software (apache for PHP, or tomcat for JSP or IIS for ASP) (just examples) are used to access these files.
now the server software needs read access to these files in order to be able to serve the file.
where as let say we are running a wordpress blog and we want rights to edit theme file from wordpress admin then we need to give webserver software write permissions.
in any case no one talks about giving other users or world users write or read permission.
now comes the tricky part.
some webserver software are considered as owner or group member of the files, but in some case its not like that
when webserver software is owner or group member then we don't need to give world users any permission. but hosts like godaddy do require giving world user write access as the webserver software by itself doesn't own the file.
I know its a bit confusing all the time.
feel free to contact me if you need help on this.