Why doesn't my iPhone available storage match iTunes?

Through settings, my iPhone is only showing 483 MB of space available. However, even after having just transferred all purchases to iTunes and syncing my phone...iTunes is showing 1.69 GB of available space. Why the discrepancy? I have no doubt that the iPhone is accurate...as I'm getting low space messages and viewing the device through Windows Explorer when it's plugged into my computer also shows just 483 MB of space. Just wondering if there could be some something eating up storage that shouldn't be that I might be able to clear out.