Well, I respect your opinion but honestly it sounds like an excuse for MS to be lazy. Being a former user of Android & iOS I can tell you right now they had plenty of apps that could edit huge file sizes & output them at the same resolution. People using SD cards taken from other cameras, stuff downloaded from the cloud, etc. Serious photographers doing serious work on their devices, tablets, etc.
Here Nokia gives us a "near dSLR" style camera in our phones & even their own software suite can't handle it. On top of that, the most res anything in the store will export at seems to be no larger than around 2400 pixels. That's kinda pitiful. I don't know if its a WP limitation of some sort or what, but still. This seems to be yet another area where MS doesn't understand how people may want to use their phones. They're not toys anymore.
Sorry for the rant, this stuff just irks me about them.