The "fast web" movement has provided a lot of tools like pagespeed and most CMS have add-ons that will speed things up. Here's a plea for the Big 3 to ship with performance enhancements by default.
According to various sites that track the usage statistics of CMSes, the WordPress—Drupal—Joomla triumvirate powers 2/3rd to 3/4th of the top 1 million and 1/4th of the entire web... If we can make these three open source systems faster, then we make the entire web faster! All three of them run fine on shared hosting. They can all be much faster when running on an optimized stack (think Varnish, memcached and so on). But the point is to make them as fast as possible on shared hosting. Src: [wimleers.com...]