Apple's just given you another reason to purchase AppleCare for your new MacBook.
Previously, the programme would not "cover batteries that have stopped working or are exhibiting diminished capacity due to normal use". This meant that if your battery stopped holding a charge, you had to fork out extra cash to get it replaced, with no other option really available - MacBooks are built to keep you out, after all.
The new terms however, are far more useful; Apple "will replace the notebook battery at no charge if it retains less than 80 percent of its original capacity", so as long as you've forked out for AppleCare, battery woes are one less thing for you to worry about.
Apple's non-removable MacBook batteries are supposed to retain up to 80 percent of their original capacity after 1000 complete charge cycles, so it's up to you whether you think it's worth the extra protection.
AppleCare also throws in a three-year extended warranty over the standard one-year affair, but if you fancy leaving the fate of your shiny workhorse to the gadget gods, then that's fine by us.