Super AMOLED consumes 30% less power because it doesn't need back light. It's also thinner. Samsung Galaxy S has 4'' screen and is cheaper than iPhone 4 (with 3.5''). Also LG is unable to produce enough IPS screens for iPad and soon part of the devices will use inferior MVA screens from Samsung. Same can happen with iPhone 4.
Samsung still has not enough capacity to supply its own lines and client lines with their Super AMOLED display. When looking in the future instead, in July 2011 they are supposedly opening a new 5.5 gen plant for AMOLED technology that will allow them an output of 30M 3" displays per month.
According to our sources, Apple had spoken with Samsung Mobile Display about the possibility for AMOLED panels since the development of the iPhone 3GS, but production capacity remains a big issue. SMD only has the capability to fulfill 50-60% of iPhone orders at the moment even it dedicated all AMOLED capacity to Apple.
Of course, cost is always a concern. AMOLED panels cost US$34-38. TN panels cost less than US$10 and IPS panels around US$20.
AMOLED also has display weaknesses. SMD uses PenTile technology developed by Clairvoyante to produce AMOLED, which is less suitable for displaying text. With Apple quite keen on pushing e-reading businesses, AMOLED may not be the best solution at the moment.
I find it very hard to believe that Apple would start using something other than IPS screens on their iPads, considering they advertise it as a feature.
AMOLED has inferior color performance, daytime viewing performance, and angle viewing performance to IPS.