The A7 and Elpida DRAM are in discrete packages next to each other, since the iPad has the luxury of more available real estate. This version of the A7 has a hefty heat sink cap on it, possibly a sign that it's running hotter than the iPhone version, and another argument for not using PoP.
In all the iPhones through the 5s, the Processor & DRAM memory are stacked on top of one another in whats called a Package on Package or PoP. This saves real estate, but limits the amount of heat that can be pulled out of the SoC. The same was true for the original iPad. But since iPad 2 the packaging has changed, the SoC is on one side of the Motherboard with a large Heat Sink attached to its top. The DRAM are located on the obverse side of the MB, under the shadow of the SoC and connected to it through the PCB.
Would be interesting to find out how it is for the iPhone Air.
Incidentally the second largest mfr.s of Tablets ( they still make the SoCs for Apple ) continues to package their own SoC and DRAM in Tablets just like in iPhones.
Wonder if it says anything about power consumption, temperature inside or sensitivity to temperature for the two groups of Designers.