Replacing a WAR file in the deploy directory performs an automatic restart of the application.
Does your build script change the timestamp of the WAR file? What happens if you copy the WAR through windows exlorer or whatever you use?
If you modify this those file .jsp .html you not need to restart your web-app.
Else if you modify those file .class or jar, you need restart your web-app
Try using a exploded deployment, then you can add/replace JSP, HTML, CSS and other static files and have the hot deployed (without having the application being redeployed).
By the way, In my ant scripts, I always create a directory withe the war contents first, and then use the jar task to create the war from that directory. Then I have two different deployment targets, one which copies over the war file, the other which copies over the war directory.