Why do i have to pay 10 dollars per year at yahoo and 3 dollars at some other company, for a domain name? It’s just the domain name right? i’m not talking about email or hosting services. When you register a domain name www.something.com You get the same thing at every company, right? so what does it matter if i get it at yahoo or at whatever place else?
Also, is it maybe so that you can’t get email and hosting at a registrar if you didn’t get the domain name from them?

To be able to sell a domain name do I need to buy the domain name in a different way?
I wonder if I just buy a domain name for example from yahoo, can I sell the name to the third party?
Isn’t that simple as buying and selling a car?
What are the important points that I should consider through this buying and reselling procedure?
Thank you very much.