Instead, web developers are quite used to this.

Web developers know that they can integrate functionality from third-parties by copying/pasting a tiny script into their HTML pages.

Some examples are:

disqus (link)

google analytics (link)

addthis (link)

It’s a great engineering work: by adding a few lines you end up with pages with conversations (disqus), with web analytics (google analytics) and with social buttons (addthis).

There is more to it: disabling/enabling the added functionality then becomes as easy as commenting/uncommenting their snippets of code.