Maven does not copy resource files - maven

Question

I have a maven web application project that follows the maven standard directory layout so I have my resource files placed in src/main/resources/.
As this follows the standard I was expecting maven to automatically add the resource files to /WEB-INF/classes of the web application during the build but no files are copied.
I have to add the following lines to the build section of the pom file to get maven to copy the files:
<resources>
<resource>
<directory>src/main/resources/</directory>
</resource>
</resources>
My question is: is this supposed to be necessary?
I was wondering if any of the build section plugins I use could somehow interfere with the copying of the resources. Are there any plugins that are known to do this?
The build section of my pom file is here:
<build>
<resources>
<resource>
<directory>src/main/resources/</directory>
</resource>
</resources>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.18.1</version>
<configuration>
<includes>
<include>${tests.to.include}</include>
</includes>
<excludes>
<exclude>${tests.to.exclude}</exclude>
</excludes>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-failsafe-plugin</artifactId>
<version>2.20.1</version>
<configuration>
<includes>
<include>**/ITSelenium*.java</include>
</includes>
</configuration>
</plugin>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>build-helper-maven-plugin</artifactId>
<version>1.12</version>
<executions>
<execution>
<id>add extra source directories</id>
<phase>generate-sources</phase>
<goals><goal>add-source</goal></goals>
<configuration>
<sources>
<source>${project.basedir}/generated/src/main/java</source>
</sources>
</configuration>
</execution>
<execution>
<id>add extra test directories</id>
<phase>generate-test-sources</phase>
<goals><goal>add-test-source</goal></goals>
<configuration>
<sources>
<source>${project.basedir}/generated/src/test/java</source>
</sources>
</configuration>
</execution>
<execution>
<id>add integration test sources</id>
<phase>generate-test-sources</phase>
<goals>
<goal>add-test-source</goal>
</goals>
<configuration>
<sources>
<source>${project.basedir}/src/it/java</source>
</sources>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.4</version>
<configuration>
<warName>res</warName>
<webResources>
<resource>
<filtering>true</filtering>
<directory>${project.basedir}/src/main/webapp</directory>
</resource>
</webResources>
</configuration>
</plugin>
<plugin>
<groupId>org.sonarsource.scanner.maven</groupId>
<artifactId>sonar-maven-plugin</artifactId>
<version>3.4.0.905</version>
</plugin>
</plugins>
</build>
Any help or information will be much appreciated.