People respond better* to seeing a cheque in their hands (the $100 a month) or a lowered price at the register (the GST) than a similar reduction in their taxes. The Bush admin took this to a ridiculous extreme with their $300 rebate, first sending a postcard telling taxpayers they were going to get a cheque, then sending a cheque.
It's too bad because they could afford to give us more if it were a refundable tax credit.
[* "better" meaning "more favourably to whomever's in power"]
=aw