That is true, most "AddOns" now days are simply smaller AddOns that have been grouped up for simplicity of installation or use.
If you are interested in creating your own AddOns for the World of Warcraft, I would suggest the following web pages for reference:
These are indispensable tools if your looking to create something from nothing. Just make sure you read through them thoroughly and understand the concepts described in the texts. I would also Highly Recommend that you read through Blizzards End User Licnse Agreement (EULA) to make sure your AddOn isn't going to break any rules or do anything "bad" that could get you in trouble.