It occurred to me that Huub wrote in gmane.os.netbsd.ports.x86-64:
>
> This is all from pkgsrc-current, 6-10-06. Why does it expect py24 while 
> it has py23? Any clue about it?

The python version selection code is dodgy at best. As a workaround, you
can put 

PYTHON_VERSION_DEFAULT=24

in /etc/mk.conf. however, you'll need to rebuild everything that depends on
python :(