Question:
Say I wanted to provide an HTML sample for copy and pasting embed tags, next to the video. If I'm going to be generating the embed tag HTML already, what's the point of having a separate swfobject.js? In my case, would swfobject.js be superfluous?


The savvy web developer uses Swfobject not just because it does the embedding, but because it does the embedding in a way that maximises the number of browsers that display it the same. Embedding is still a rather dark art and swfobject ensures you don't have to be a psychic to predict what browser your visitors are using.
Another important feature is that Swfobject also supports the provision of alternate content for users without JS or Flash installed/enabled, so that a pleasant, helpful message is display to try and improve installation and viewing of your video.
The point of still using swfobject therefore, is because you want users to view the videos on your site, right? Swfobject helps ensure the maximum possible number of users will see the video and if they can't see it, they'll be told how to see it in your 'alternate' content.
Its one thing if users can't watch the video after someone has cut and paste the embed code you provide onto another site, but its a complete fail if users can't even seen the video on the origin site!
Sites that provide users with bog-standard html tag embedding, do so not because that method is sufficient (far from it) but simply because its ridiculous to ask users to do it this advanced way.