Try creating an XPage in a new database and adding some basic HTML. By default it will include only 3 CSS files (based on the default "webstandard" theme) and 2 JS libraries (dojo.js and xspClientDojo.js). If you change the theme of the database to your own, no CSS files are send by default.
It all depends on what you add to the XPage. If you increase the complexity (e.g. by adding custom controls), the number of included files also increases, because most of the custom controls rely on additional (dojo) libraries/ CSS.
Try creating an XPage in a new database and adding some basic HTML. By default it will include only 3 CSS files (based on the default "webstandard" theme) and 2 JS libraries (dojo.js and xspClientDojo.js). If you change the theme of the database to your own, no CSS files are send by default.
It all depends on what you add to the XPage. If you increase the complexity (e.g. by adding custom controls), the number of included files also increases, because most of the custom controls rely on additional (dojo) libraries/ CSS.