Why don't you open an apple store in iran iPhone 4

Nobody here works for Apple or can comment on Apple's decisions.

How can i find my answer?

You don't. Only Apple would know their reasoning, and they rarely/never comment on such decisions. If you would like to try to contact them, there is a contact us link at the bottom right of this page.

US laws prohibits export of just about any product to Iran, so Apple is legally barred from selling their products there and will be until such time as there are major changes in US policy, not likely to happen in the foreseeable future. If you wish to read up on US sanctions, see:

http://www.treasury.gov/resource-center/sanctions/programs/pages/iran.aspx

Sorry, but you will have to take your iPad back to Dubai to get it serviced.

Regards.