Your (and others) comment is about income and taxes paid only. However, the US tax system is not just about income and taxes paid; it is also about deductions and tax credits. Yes, the IRS can calculate accurately (based on company reporting/history) what you've earned (income) and paid into the system for the tax year (taxes paid). Is that all you want them to do though? Of course not. Anyone who says, "Yes!" to that simply hasn't either thought this through or doesn't understand the concept of tax deductions and credits. See my comment above for more detail.
I think that, while the "5 minutes and you're done" thing can be understood as marketing spin, it would not be tremendously hard for any IRS service to provide the same kind of itemized listing that most tax softwares do to handle credits and deductions.
My tax experience is light–it takes me maybe an hour of data entry after all my stuff is gathered–so this wouldn't actually help me at all. But for others? If you could shave off as little as 20% from time spent on taxes, that sounds worthwhile to me.
