Code Review

I got my first code review on a theme I submitted and I have some questions. The first is on the following line.

* Only enqueue admin stylesheets and scripts using your Theme-specific
page hook.

I can not find any reference to a Theme-specific
page hook. If my theme is called xyz, what would the Theme-specific
page hook be called?

2011 uses the following line:
add_action( 'admin_print_styles-appearance_page_theme_options', 'twentyeleven_admin_enqueue_scripts' );
If is ok to use the ‘admin_print_styles-appearance_page_theme_options’ hook?

I included the following line in the header.php.
ob_start("ob_gzhandler");

I was told “* GZipping content is Plugin Territory”. It seems odd to make a plugin for one line of code. I can not find any reference to what is and is not Plugin Territory. Can someone please point me in the right direction?