Sure, it'd be easy in a perfect world for the IRS to handle everything, but it'd require absolutely no unexpected deductions. The whole point of those deductions is (ostensibly) to make taxes more fair, so why should we encourage undermining that fairness?
The way it works where I live (small European country), sometime in March I get a letter with the number the tax office have been given, and a calculation of much I owe or are due. If all the numbers are correct, I do nothing, as doing nothing by May 1st is defined as accepting the numbers. If there are deductions missing, I log in to the tax authorities web site and add the missing numbers (can also be done on paper). It also lets me upload documentation in the form of scanned documents. If originals are required, they are sent by mail.
After the tax office have redone the tax, I will then get a new letter with the recalculated tax.
Pretty simple, and works nice. No taxes needed to change to accomodate the new system.