Nokia is experimenting and following the well-known "release-early, release-often" policy. This includes throwing out new devices with experimental features (webcam, FM-radio, great speakers, light-sensor, GPS, keyboard, ...). But selling to a broad base can be counter-productive. If the products aren't mainstream-ready (we all know that they're not yet ), the mainstream people will remember to avoid the products.
Nokia sells the tablets to power users at the moment, and that's their current target audience for the tablets. Eventually there might also appear NITs in the E series (with PIM and all that stuff for enterprise users).