Try telling that to developers; they love using S3 as both a database and a filesystem. It's gotten to the point where we need a training for new devs to tell them what not to do in the cloud.
Communicating through the filesystem is one of the Classic Blunders.
It doesn't come up as often anymore since we generally have so many options at our fingertips, but when push comes to shove you will still discover this idea rattling around in people's skulls.