Subtheming not possible

I'm a bit confused on how to subtheme or customise zeropoint.

The CSS files are added in the template.php rather than in zeropoint.info so if I subtheme I find that the subtheme css gets added before the base theme css so doesn't override it. There doesn't seem to be anything later than preprocess_html function I could put in the subtheme template.php. I've tried mysubtheme_preprocess_html(&$vars) and then having that do

zeropoint_preprocess_html($vars)
drupal_add_css(etc.

But that doesn't work as the function get_zeropoint_style inside the zeropoint_preprocess_html function. If I move get_zeropoint_style outside the function then it is happy

You say to use _custom/custom-style.css and make changes there, then to rename that file to stop updates reversing any changes. But as far as I can see if the file name is changed it doesn't get loaded, so that doesn't work

Also, another bug, in custom-style.css you have .sizer when it should be .sizer0.

It would seem preferable to follow Drupal's recommend route and subtheme in order to override or even just to add new templates. At least that way all the customizations are in a separate folder and zeropoint can be upgraded without any adverse effects.