As far as I know, these days all modern systems come with Perl 5.14+ at least.
Not everyone has the luxury of working on modern systems.
This century I've seen Perl 5.8 on board of Solaris only.
5.10 wasn't even released until the end of 2007 therefore everything released before that will have used 5.8 or an even older version. RHEL5 used 5.8 and some of those boxes are still supported under ELS.
All that said, I don't see much value in supporting (or trying to support) anything older than 5.8 for any new modules written today. The stipulation about ::Tiny was put in place years ago and time doesn't stand still. Perhaps the new steering committee could look to revise the official guidance once they are done with Perl 7.