The IRS sends you a form with all the numbers filled in. After all, for many people, the IRS already has that information.
Here's Norway's version:
"You will receive a tax return from the Norwegian Tax Administration in March/April if you work in Norway or on the Norwegian continental shelf. The tax return gives an overview of your income, deductions, assets and debts for the last income year.
You must check that the information in the tax return is correct and complete. You do not need to submit it if there are no changes to be made."
http://www.skatteetaten.no/en/International-pages/If-you-wor...
The system many other countries have, such as the example given for Norway, involves them filling the data you intend to give to them. If you supply your own data then you may have to give proof. I don't see the difference in what they end up knowing.