The fact is, the iPad has a much better screen. Period. I don't see how anyone can enjoy watching a movie on a 6-bit TN display.
It's higher quality in terms of color accuracy, but it's also much smaller. What do people buy for their wall, an extremely high quality 30" ACD with an IPS panel, or a 50"+ LCD? Size is more important to most people than extremely fine details which most people cannot see a difference in.
In addition, movies are NOT typically better on an IPS display. The color will be more accurate when still, but the response times would be inferior as well as frame rates on the IPS displays. IPS displays are not superior for motion of images on the displays, they're superior for still photos, crisp and sharp edges, and excellent color reproduction. They're used on high quality displays for WORK in 3D modeling, color accuracy, and extreme clarity, NOT for watching movies.
The most likely reason Apple used an IPS display on the iPad was for the viewing angle problem of TN displays. Think of
sharing an iPad video if it were a TN display, it wouldn't do as good of a job. However, a computer by its nature is a one person machine, which is why a TN display does the job just fine. Apple knows what it's doing. In addition, the TN displays Apple uses are some of the highest color gamut displays that excel far beyond the normal or average of TN displays. Apple also uses LED backlighting for an incredible experience far different than a normal TN display you might see in a netbook or PC counterpart. The reason Apple uses these on the Mac notebooks is to take advantages of ALL of the uses a Mac user would need the display for. Realistically, a pro would probably prefer an IPS display and not for watching movies, but then most pros couldn't work on any Mac notebook. Most real "pros" who need a professional grade workstation use PCs with IPS displays or Mac Pros with a 30" ACD IPS display. Or these pros connect their MBP to a 30" ACD or NES (IPS) display for "professional" work.
I would much prefer an IPS display on my MBA, but I want it to be 13.3" and NOT 9." In addition, I want the IPS display for the entire workload I use the computer for, NOT specifically for the videos I watch.
If Apple's sole intent for the iPad was video playback for oneself, it would have been better off using a different display. The IPS display is excellent for stuff like reading and clarity of still images/photos on the iPad. The IPS display is excellent for viewing angles as the iPad is meant for sharing with the family. Apple envisions an iPad in every home on the coffee table shared by all. A computer is normally a one person interaction between him/herself and the computer.
Understand why you have an IPS display... it's not for the video playback for one person to watch a movie. It's for viewing angle capabilities to be shared, crisp viewing of family photos, excellent reading, perfect color reproduction, so your point of it being there for video playback for yourself is probably an incorrect point to make for the iPad. Say you are sharing a video on a plane with your spouse, better with the iPad if you can get away with sharing a 9.6" display. The display is also a higher quality display because it's meant to be held extremely close to the eyes which is different than TVs, computers, or Mac notebooks.
Apple uses the right displays for the job/device given the complete purpose of the device by most users. I would prefer an IPS display in my MBA next time but the average user wouldn't notice the difference or care too much because they're not using their MBA for things that an IPS display is superior at. You have to admit that Mac notebook displays are pretty incredible for their uses... I admit that the IPS display on the iPad is incredible, but I have to be sharing it with someone else for video playback or reviewing photos or reading with the iPad close to my eyes to notice the difference vs a TN, high color gamut, LED-backlit display like Apple uses in the Mac notebooks.