Constraints in design can never be avoided. Every problem has a context, and every context has its own unique set of constraints. So it is with web development. Early websites were simply static HTML pages that you requested from the server. Each new page you go to is a completley new request with completely new HTML. Sites began implementing layouts on websites that kept consistent headers and footers across all pages. So although users are seeing the page go blank and then reload, sites would still attempt to create a smooth experience thoughout.
Now, in 2012, not much has changed. Sure, we have more friendly routing and much faster page loads, but the experience has remained roughly the same. For every new page a user navigates to, the browser window goes blank and a completely new page is rendered.
With the introduction of AJAX, and its popularization by libraries like jQuery, the web has seen a giant leap in development. Single page applications have been built that are able to recreate both the functionality and the experience of native desktop apps. These applications have consistent navigation, and using AJAX and Javascript the app will render new pages and update data without re-rendering what doesn’t need to be re-rendered. This is the web of the future.