The only real REASON to switch to 48 is related to the move toward 3D, though. 24 works just fine in cinema as it stands today and has for decades. Somebody noted that they thought the film looked more artificial when they turned off the interpolation on their TV, but art IS artifice; it can never be reality, no matter how hard it tries. The fact that it looked more artificial is not at all a bad thing. Indeed, making film more "visceral" and "engaging" can be a codeword for "spoonfeeding the audiences everything instead of making them do a bit of work." This is not like the switch to sound or the switch to color, which were incremental changes on the same basic idea. This is a change to the fundamental foundations of cinema, and I don't think that it's being done for reasons that are at all artistic, merely commercial.
Edit: PD: T1/T2 and Aliens prove that Cameron can be an excellent, non-soap opera director. Maybe not anymore, but once upon a time.