There are a few big sites that use Chevereto as is and other use it as a base. If you can save money with a good base you will. That's why people use frameworks or CMS. I could say a dozen of big websites with huge traffic based on Wordpress, Magento, etc. You go to own software just when there is no base that you can apply or when the high resource usage push you to develop wild things like facebook or mailchimp. But everyday you will find that everybody use something from someone else... A class, a complete script, etc.