In reply to Piet.

I think it's a bit more nuanced then "it's all Envato's fault". While some responsibility lies with Envato for allowing such an environment where this issue can occur, I feel the majority of the responsibility lies with the theme developers who should know about the risks of using third-party code in their product that they sell and are supposed to support. If you include third-party code/functionality in your product that you sell, you better have a way to support it. Finally website owners have a responsibility to keep up on the products and services they use on their WordPress sites - you just can't throw it up on the web and ignore it. If they had a developer help them set the site up, it behooves the developer to provide a list of what themes and plugins are being used and to educate the site owners on how to ensure that they keep up-to-date.

To conclude:
1) Envato needs to encourage a better theme environment (which they are starting the process of doing) to avoid these types of issues.
2) Theme developers need to make sure that if they include third-party code and functionality that they have a way of supporting it
3) Buyers of themes need to stay up to date with what they're actually using on their site. Ignorance is dangerous.