Its very possible. The bulk of storage on my phone that is being taken up is from backups. I always keep about 2 backups, its a chunk no doubt. But, it just looks like you have a lot of music, movies, pictures from the screenshot. I have been using Google Music so I don't have to store any music on my phone, and its a saver.
Do you have Astro or have mounted it to your PC? With Astro or connected to your PC, you can go through the directories. There can be lots of stuff, like crashdump info located in /debug, that use space but don't show up.
If you use a browser like Dolphin, it can store cache info on the "SD Card" [its description]. Try clearing cache info your browsers or any other apps that have might make use of cached files.