You can disable commenting on specific pages using the user interface in the WordPress dashboard. You go to Pages>All Pages, hover over the page name so the dropdown menu appears, and then click Inline Edit for the specific page. There is a checkbox for “Allow Comments.” It’s checked by default; simply uncheck it and save. You have to repeat this for each page you want to disallow commenting on, but it’s a straightforward way to deal with it in the UI without messing with php, and still allow commenting on some pages.