I'm not saying that my goal is for instance support apache v1, the goal is support nginx, apache and lighttpd.
And also, support MySQL, Postgree, MySQLi, etc.
That is because you may know that mysql is not the ideal thing to use on a large site. Also, I want to support APC or other types of caching.
So, the thing is that you need a lot of benching, a lot of test, a lot of reading also. To give you an example. Curl was used instead of file_get_contents after a lot of test and real benchmarks. Stand alone benchmarks and in script benchmarks. That leads to the election of curl.
The same thing happens with all the libs and functions, they are really tested and tested. Even in loops or other small things the script is improved over and over... So, apache has mod rewrite, nginx and other servers don't understand it so it must be worked out... The way that the servers handles the "php" may be the same, but you can't assume that something that works on apache will work on the same way on other server. It just doesn't work that way.
By the way, the script pretends to be used from the small personal usage to the large image hosting site. So, you must support shared environments because there is people who just want their own personal image hosting (it was the Chevereto's punch line since the beginning)... And the number of people who want this for personal or reduced usage like for their own community or website is huge, way more than the people who wants to use this as a large script for image hosting.
In fact, in the roadmap the last stages aims to the large production site. A large site does also need improved server configs, highly tested and optimized... Don't be surprised if you see in the future a "Chevereto Pro" release because the work that is needed to be made is quite huge and you are dealing with thousands and you need to re-tune the server model to make it fit all your needs.
Don't think that a VPS is just the top of the top and that with one of them you are OK, mostly VPS won't be able to handle a large production image hosting website.