Think of broadband as the same as a land line telephone, and wifi as a cell phone. I think 3G is wirelss also, but I am unsure of how it works technically. I am perfectly willing to accept it as magic.
The instructions say that you can download it to your pc, and then upload it to the Kindle. Yes, you can also then delete it from your pc. This is what I was trying to do without success.
Unless you have a laptop that you want to be able to connect to the internet with from anywhere in your house, you probably do not need a wifi router.
I'm with you, and hope some of the techno-wizards who see this can help.