[development] why not just phptemplate in core?

Hello, I have one question. Why do we ship a plain PHP theme in core? Wouldn't it be good for consistency if all themes would be a phptemplate theme? and wouldn't it be easier to maintain a phptemplate theme as a plain PHP theme? Is there any reason why chameleon is plain PHP? I think it may confuse people that we ship a theme where the code is not similar compared with all other core themes. cu Tobi btw. I converted the chameleon theme to phptemplate: see http://drupal.org/node/41005