Desktop applications such as QGIS and ArcGIS have the luxury of running on desktop hardware where 8+ gigabytes of RAM is quite common. iPhones and iPads on the other hand are somewhat more constrained, 1GB of RAM is still quite common and only half of that may be available for an application to use. Furthermore, iOS applications that exceed memory limits will be terminated by the operating system, a situation best avoided.
Usage scenarios are also expected to differ across mobile and desktop. While a desktop user may be happy to launch an hour long background process to download multiple gigabytes worth of Landsat data, mobile users would likely not. A mobile user should in 5 minutes be able to do what they need.
ObservedEarth was developed around these constraints.
The preview image visualisation is download as a low resolution JPEG image; while it can be cropped, doing so will not increase the resolution of the image data displayed.