Seam is not specific to JBossAS. You can run Seam in any app server.
I particularly like that fact that the View and Model are more integrated. I very much disliked, in Struts, having to use one bean to hold form data, and then to copy, and possibly convert, that data to another bean (typically, a DTO), which was then given to the data (where the data was copied yet one more time). Not only does copying data from one place to another slow the application down, but it also tends to generate more garbage which then has to be collected.
Also, just because the View can make use of the Model objects directly does not mean that MVC is broken.
JSF follows a more traditional GUI-application MVC pattern, whereas classic Struts follows an MVC2 pattern which is a variation of MVC that is more page based than component based.
Seam acts as the glue between JSF and EJB (and other technologies) allowing you to use an object that has already been populated by one framework in another without having to create copies of you objects or create parallel class hierarchies.
There are several presentations / demos available on the Web. Take a look, and then try to build something yourself and see how you like it.
It's ok using MVC, design patterns and all, But we should not lose focus of the task that we want to achieve. e.g.,We use DTO to transfer data between the layers and to improve performance. While this is correct in theory, very rarely do we make remote calls where this pattern is really needed. AFAIK majority of the applications do not use remoting. So if Seam allows us to reduce some layers, there's no harm in it. If anyone is comfartable with Struts, they can of course continue to use it. Also refer to Martin Fowler's treatise on Anemic Domain Models at his website.