I seriously doubt that the update is ISC, Motorola has already ticked a lot of their Atrix users off by posting that ISC was coming to the Atrix 4G for months and then at the very last moment deciding that the Atrix 4G was going to stay on Gingerbread. It is most likely either a set of fixes or the soak email was sent to Atrix 4G users by mistake and was meant for either the Atrix 2 or Atrix HD users.
I enjoyed the Atrix when I had it, but got really burned by Moto's long delays in updating the XOOM Family Edition to ICS and the way they toyed with the Atrix users. I certainly was not going to buy another Moto phone.
Sorry for the sour grapes, the Atrix is such a good phone with many innovative features and deserved better from Moto.