The point is no ones sure, nVidia itself has not released dates as to when Tegra based chips will start flowing in enough nos. that it'll be able to start delivering them into the market, rumors abound of low yields from the first silicon wafers put in fabrication.
Also the last time this happened, the nVidia GTX 4** series was ~ 4 months late in the coming and all the cards reinforced that the Fermi chip was not fully matured, the power draw and corresponding performance was not justified. So nVidia had to wait for the GTX 5** series release to fully capitalize on the power of the Fermi architecture.