They assume that your vehicle is regularly serviced at the dealer, of which they should always check the battery level for you. If you're not driving the vehicle, a battery maintainer is always plugged in to maintain a charge.
There is a way to get to the emergency frunk release cable, so it's not the end of the world...
When my battery died last winter it still had enough charge for the windows to roll down and for me to open the frunk. I replaced it with an Optima redtop.
Here are some useful tips/info on dead battery on boxster:
http://sites.google.com/site/mikefocke2/whenyourbatteryisdead