I've been reading two books about web usability issues and tests (Rocket Surgery Made Easy¹ and Prioritizing Web Usability²) and they claim some strategies and typical problems about website usability and how to lead them. However, I want to do a web application, and I think I lost track of what I am trying to solve.

These two books claim to work with raw websites (e-commerce, business sites, even intranet), but I'm not sure if everything about web usability is applicable to web application usability.

They sure talk about always having available (and usable) the Back button, to focus on short information rather than big amounts of text, etc., but they could be inaccurate in deeper problems that may be easier (or just skippable) in regular websites.

Has anybody some experience in this field and could tell me if both web applications and websites share their usability issues? Thanks in advance

Edit: Quoting Wikipedia, a website is a collection of related web pages containing images, videos or other digital assets, and a web application is an application that is accessed over a network such as the Internet or an intranet. To sum up, both shows/lets you search/produce information but websites are "simple" in interaction and keep the classics of websites (one-click actions) and the other one is closer to desktop applications in the meaning of their uses and ways of interaction (double click, modal windows, asynchronous calls [to keep you in the same "environment" instead of reloading it] etc.). I don't know if this clarifies the difference.

Edit 2: Quoting @Victor and myself, a website is anything running in your browser, but a web application is somewhat running in your browser that could be running in your desktop, with similar behaviors and features. Gmail is a web application that could replace Outlook. GDocs could replace Office. Grooveshark could replace your music player, etc.