Just about _everyone_ has the shared IP of the server their account is on. Unless your site is going to have a shopping cart, etc. you don't need an IP all to yourself. There is no reason..
GoDaddy specializes in domain names and can offer them at a cheaper price than we ever could. We cannot afford to charge so low for them.
If you don't want to register a domain name, that is fine. But you'll have to input something into the domain field, even if it is not your domain. You can put whatever you'd like as the domain. You could put dontknow.com
What is important though if you don't choose a domain name, is what you choose as your username.
You will access your space by going to
http://216.67.243.52/~username-of-your-choice