Strictly speaking this is not true, WordPress is possibly the most popular blogging platform right now ( and gaining weight as a CMS ) and it's themes are php.

However if you insist on another layer than PHPTal & Smarty would be your best bets. I personally prefer Tal but it's not as user friendly as Smarty ( This is based on a survey we did of our customers and their attempts to customize their templates ) so if you're going for the masses it'd be best to go with Smarty as it's sort of a defacto templating engine

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