The big difference between Premium and Pro and/or Standard version is, If you buy Premium script then you will get source code. While on Pro or Standard script, you won't get source code.
Another common difference is that if you buy Pro or Standard script, We will provide server hosting for your domain. We will provide hosting until your purchase license exist. If you want to host site on your own server, you have to purchase Premium script.
To see more difference between Premium, Pro and Standard version, You can click on "Pricing" or "Details" button on Products page.