appengine-web.xml used to have this static-files section, which was only explicitly specifying static content.
<static-files>
<include path="index.html" expiration="30d" />
<include path="bitdual/**.cache.*" expiration="30d" />
<include path="bitdual/js/*.js" expiration="30d" />
<include path="votesmart/**.cache.*" expiration="30d" />
<include path="votesmart/js/*.js" expiration="30d" />
<include path="*.gif" expiration="30d" />
<include path="*.png" expiration="30d" />
<include path="*.html" expiration="7d" />
</static-files>
<resource-files>
<include path="bitdual/*.gwt.rpc" />
<include path="bitdual/*.nocache.*" />
<include path="votesmart/*.gwt.rpc" />
<include path="votesmart/*.nocache.*" />
</resource-files>
I replaced it with the following, which is the newest default config generated. Note that it specifies the world as static first, then gets more specific.
<!-- Configure serving/caching of GWT files -->
<static-files>
<include path="**" />
<!-- The following line requires App Engine 1.3.2 SDK -->
<include path="**.nocache.*" expiration="0s" />
<include path="**.cache.*" expiration="365d" />
<exclude path="**.gwt.rpc" />
</static-files>