do other car audio manufacturers also use this bus link stuff or are they easier to work with?

You have to understand that "this bus link stuff" is for CD-changers only. It's not meant for Aux-in. There is a such thing as car stereos with Aux-in, but that's a different feature than a CD-changer input.

They do that on purpose. It's not like the audio inputs on the CD changer connection are any different than an Aux-in would be, it's just that they want to make you buy their brand of CD changer, so they use a proprietary connection.