Warner Bros recently explained its decision to limit its rollout of The Hobbit: An Unexpected Journey at 48 frames-per-second to Deadline. The 3D at 48FPS tech, which WB calls "HFR" for High Frame Rate, is being rolled out slowly because there are glitches that need to be corrected and "This is a technology that is going to change the way people see movies…You have to do it right."
New tech has glitches, that is to be expected. Another issue is cost. It seems that the cost of turning a screen into HFR ready can cost $5000 per projector and as high as $20,000 for IMAX. If the projector was recently purchased, there is still a $1,500 cost for the software upgrade. This does not include the faster bulb burn out rate and the high cost of replacing them.
It seems the plan is basically to use The Hobbit as a proof of concept to encourage studios to start paying out for the upgrade. The more that upgrade, the more the tech can be perfected and the faster the cost will drop. This means that The Hobbit has to get it right the first time as unlikely to be any second chances if audiences do not like the experience.