Why do such things need to be hosted at all? I've got a few file converter apps on my laptop. They're faster and better and you don't need to stream the data off somewhere just to process and stream back, which is silly.
A relevant audience are the corporate computing inmates, who cannot install anything locally... They are happy to find utilities wrapped behind some web front.
An often missed driver for the cloud-ification of everything is that it offers a way to escape corporate IT. Sending a 20mb file 2000 miles away to do something trivial to it and send it back is easier than getting permission to install an app.