Paying taxes doesn't mean just paying federal taxes. Users don't want free Federal taxes software if it means they'll have to re-renter all their information into different software for their State taxes -- especially when more than one state is involved, such as for people who cross state lines for work, or moved mid-year. A tax service is a massive value add.
The "free" software you get to do your federal taxes will be no threat to TurboTax until the states are required to publish their tax codes in the same machine readable format as the feds.