Because it is always wise to let early adopters discover any problems with a patch. A few are being reported in this case, not just a lack of a fix for battery problems, so it is sensible to wait a day or so for the reports to come in to see if they are likely to affect you. There will always be plenty of users who just must have the latest thing as soon as it comes out - let them discover any potential flaws.
This applies to patches to any operating system - Windows, OS X, iOS, Linux, whatever. Always let the impatient take any hit. It's basic computer management. If you've ever had to manage patches for hundreds of computers you'd soon understand why this is received wisdom.
It also applies to new hardware. Let the really impatient find out if the latest thing is the best thing since sliced bread or a lemon. What does it matter is someone else gets the latest gadet a day or two before you?