Maybe they want to avoid sending checks to households that did not receive the letter.
OK, so if they send out a letter and it comes back as undeliverable, they will not send out the check. The idea is that the check might get in the wrong hands. Of course the taxpayer would still be entitled to the money, but he might need to inform the IRS of his valid address before the IRS would mail out a check. I wish the IRS would just credit my bank account like they do with most refunds.
Are you sure it is just a letter. Maybe they include a form that allows the taxpayer to specify that he would like his rebate direct deposited to his bank account.
I'm always amazed at people who complain about government waste, but ignore the incredible amounts of money wasted by the military machine. We have a far larger military than we need for national defense.