Would ask for some briefing session, but I would guess thats not the right forum for it, talk to your contacts within Cisco.
Did you check out:
https://supportforums.cisco.com/docs/DOC-26316
So sure, things enhance, so the easiest answer which will match: enhancements and the vendor sais so.
Should be enough :-p
The key words in that guide regards the MEP would be "Uses B2BUA functionality".
If I interpret it, it is two different call- or at least media legs, doubling up the port usage for these calls.
If you have a customer with 5 traversal call licenses you would most likely not need to change it.
I think its a bit strange that Cisco changed it by default as this can easily break existing firewall configs,
I would have made an alert for systems which have licenses were you might reach that limit stating
"to utilize the full licenses with MEP, please change your port range to: *number* and fix it in your firewall, ..."
and sure the standard documentation (release notes, admin guide) are always a good source.
