The initial release for 5.10 has some serious defects. I don't consider 5.10 old enough yet to be fully vetted. The reality of the Perl releases are that 5.8.8 hung around for a long time, so the majority of modules work with this version and have not been updated since. In addition, a lot of the non-Microsoft operating systems come with 5.8.8 or near, echoing my sentiments.