Many Spring components depend on log4j directly or indirectly and the POM produced by Roo expects log4j. However there is no default log4j configuration file so you always get log4j warning messages at start-up - like this:
log4j:WARN No appenders could be found for logger (org.springframework.test.context.junit4.SpringJUnit4ClassRunner).
log4j:WARN Please initialize the log4j system properly.
Auto-generating a default log4j config file would be very useful and remove the ugly warnings.