This is what the JEE 5 spec says about deployment in Section EE.8.4 (Deployment)
Any Java EE product must be able to accept a Java EE application delivered
as a .ear file or a stand-alone Java EE module delivered as a .jar, .war, or .rar
file (as appropriate to its type).
I think that what Abhay was originally asking wasn't really why is no WAR file created, but why no exploded WAR directory was created. Not totally certain, because he was asking about things as though they occurred in the opposite order that they really do.
Tomcat, as well as quite a few other appservers, allows deployment of webapps in "Exploded WAR" format, which is simply the set of directories and files you'd get if you unZIPped a WAR file. Since Tomcat isn't full-stack, it doesn't deal in jar, ear or rar deployables, so I won't mention them further.
However. this is just a convenience. Nowhere in the JEE spec will you find reference to exploded WARs. Officially, to be deployable, a JEE webapp has to be a single WAR file (or EAR, or whatever). Furthermore, Tomcat is under no obligation to actually explode deployed webapps. The option is turned on by default, but it can be turned off or even not done because of how the war was deployed, and I do have some production webapps that don't explode their WARs, in fact.
So just to set the record straight:
A. Tomcat, like other JEE webapp servers does not produce, WARs, it consumes them (as you pointed out). Furthermore, it can work with WARs in their original form, explode them, or accept them in pre-exploded form.
B. IDEs and build utilities such as Ant and Maven can build deployable WARs. I'm not familiar with the Sun deployer tool, but assuming that it lives up to its name, the Sun deployer tools would not be building WAR files, it would be consuming them, bundling them with their corresponding appserver-specific deployment descriptor (if needed), and then forwarding the results through a suitable deployment mechanism (such as JSR-88) into Tomcat. Whether Tomcat then explodes the deployed WARs, like I said, is ultimately Tomcat's decision, although it's possible that the Sun deployer tool's specific deployment processes influence Tomcat's decision.
An IDE is no substitute for an Intelligent Developer.