Hi!
First of all, the servlet implementation class and the second deployment descriptor file you talk about are both specific to the GlassFish server and cannot be used with other servers.
When using JAX-WS, it is not necessary to use the web.xml deployment descriptor - rather
you should rely on using annotations for configuration.
Yes, you can use the web.xml deployment descriptor but experimenting with it has caused at least me some hassle.
Thus, I recommend staying away from these files until you gain more knowledge.
I have written some about web service deployment in my SCDJWS study notes, if you are interested. They are available here on JavaRanch.
Best wishes!