I dont think you frequent the FMA sub-forum often but just letting you know I posted the final FMA:B character poll and theres a spoiler in it for anyone who's only watching the dub and its a biggie so stay away from that thread for a while.
I was going to mention imbehindyou's work. It's partly the nature of the theme. As a theme, flight feels liberating to the soul and simplicity often conveys that same sense of liberation. So people are unconsciously responding to that. Cluttered pictures take away that sense of liberation.