Weight of RWC players

Scrapping various Web pages I managed to gather data on players participating in last 4 Rugby World Cups. Is there a trend in body mass of rugby players participating in RWC tournaments?

Using Plotly API via Perl script (described here Box-plot chart with plot.ly and Perl API) I can quickly plot series of boxplots:

# cpan install WebService::Plotly in case  WebService::Plotly is not installed
plotly_boxplot.pl -col=5 -by=0 -title='RWC players by weight' -sep=';' rwc1999-2015.csv

Resulting boxplots and data can be viewed here.