Apple's just given you more reason to purchase AppleCare for your new Mac. Where previously the terms stated it would not "cover batteries that have stopped working or are exhibiting diminished capacity due to normal use", the new terms will replace a battery that holds a less than 80 per cent charge.
The new, updated terms now say that Apple "will replace the notebook battery at no charge if it retains less than 80 percent of its original capacity" so long as you have your laptop covered by AppleCare.
Apple's non-removeable MacBook batteries are supposed to retain up to 80 per cent of their original capacity at 1000 complete charge cycles. Being non-removeable means it often costs a pretty penny to have them replaced if they're out of warranty or have finally stopped charging properly. Having AppleCare extends warranty coverage to up to three years after purchase, without which the notebook will have a limited one-year warranty and 90 days of free phone support.