There’s nothing preventing you from having routes like resource/id with HTTP methods GET/PUT/POST/DELETE in ASP.NET MVC. It’s not the default routes setup but you can do it.
EDIT (MLaritz – Adding Darin’s comment):
ASP.NET MVC is a server side technology allowing you to expose RESTful urls. The way they are consumed doesn’t matter. You asked about why ASP.NET MVC is considered RESTFul technology and the answer is because you can easily expose RESTFul urls for consumption, it’s as simple as that.