In 2012 (the last year for which I have a breakdown: https://www.irs.gov/pub/irs-soi/12rswinbulreturnfilings.pdf ), of the 239 million returns filed, about 143 million are individual returns. Of the 143 million individual returns, about 13% or 18.6 million use 1040EZ ( http://www.freeby50.com/2012/12/what-percent-of-people-file-... ).
The IRS probably has enough information to file 1040EZs for most people, but certainly not enough for 1040A, 1040, or most business returns.
So, of the 293 million returns filed, about 18.6 million or 6.3% of them could be auto-filed by the IRS. About 1 in 16 total returns and about 1 in 8 personal returns.
To me, 6.3% (or even 13%) is a far cry from "all the typical cases". They can mostly handle one particular case; that might be the case that you personally have; I have no objection to them offering that as a service. Just don't be confused and think that that that's all the typical cases.