For Web Applications: Web application can be implemented using any kind of technology like Java, .NET, VB, ASP, CGI& PERL. Based on the technology,We can derive the components.

Let's take Java Web Application. It can be implemented in 3 tier architecture. Presentation tier (jsp, html, dthml,servlets, struts). Busienss Tier (Java Beans, EJB, JMS) Data Tier(Databases like Oracle, SQL Server etc., )

If you take .NET Application, Presentation (ASP, HTML, DHTML), Business Tier (DLL) & Data Tier ( Database like Oracle, SQL Server etc.,)

Client Server Applications: It will have only 2 tiers. One is Presentation (Java, Swing) and Data Tier (Oracle, SQL Server). If it is client Server architecture, the entire application has to be installed on the client machine. When ever you do any changes in your code, Again, It has to be installed on all the client machines. Where as in Web Applications, Core Application will reside on the server and client can be thin Client(browser). Whatever the changes you do, you have to install the application in the server. NO need to worry about the clients. Because, You will not install any thing on the client machine.