The future cost of foregoing the tablet user, or more aptly termed by Peet, the cell phone "companion device" user is exposure.

In addition to the millions of iPhone users now there are millions of iTouch users.
The iPhone GUI will be more acceptable to them than other alternatives as a front end for controlling dumb appliances that are now evolving with built in connectivity.

I believe a companion device will still shake out to be a viable market. It may eventually be larger than the whole "smartphone" market combined, as evidenced by GK's post.

People may begin to realize that taking that expensive smartphone with them everywhere when at times they just need access to a cell phone, may not be very "smart" at all. And that loosing or breaking one half of their communication electronics is cheaper and easier to replace when traveling and has less negative impact on productivity.

Where the iTouch looses ground however is BT DUN. The Nokia tablets played nice that way.