In a Nutshell
Web applications cannot perform client-side processing and still be compliant with Section 508 and other accessibility guidelines.
Client/Server applications are “rich clients,” in that they allow for more complex graphical user interfaces and the use of client-side processing. COM, DCOM and Active X all allow client-side processing in a Microsoft environment. The limitation of the Client/Server approach is that they can only reach to highest level of where the application is hosted.
Web applications are a low-cost, broad-reach approach that provide access to information and applications from wherever the user is located. Unlike Client/Server apps, Web apps are “thin clients.” The drawback is that Web apps limit the user experience by turning the client computers into “dumb” terminals. Web applications cannot perform client-side processing, and still be compliant with Section 508 and other accessibility guidelines. Data must be transferred to the server via an HTTP request, so elements of the Client/Server user experience are lost. Examples include direct manipulation of data, such as dragging and dropping elements and client side-processing and storing data locally.