If content of a Web page changes with user's action/request and with time, we use PHP. It is less sense to use PHP, if content of Web page remains static. Also, idea is to update HTML of a Web page using PHP whenever it is needed; as they ( Webmasterworld ) use CGI and update/write HTML page, when needed. So users are served static Web pages ( .htm or .html ), but PHP updates/writes into these Web pages, whenever required/commanded. In other words, such Web pages don't generate content on the fly or merely on users' request, but on Webmaster control. Hope these ideas'll help you.
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