This has nothing to do with file allocation tables; different measurements (the 4.38GB indicated as free space is indeed 4.38GB in "computerese" (1GB = 1024x1024x1024). In "disc-drive-maker-ese" it would be 4.7GB; nor any extra formatting for a standard DVD.
The stated capacity of a DVD INCLUDES the normal overhead associated with lead-in and lead-out for the DVDs ==> i.e. you can absolutely write 4.38GB of data to the disc.
What is almost certainly happening in your case if that you have a packet-writing utility installed, which treats the DVD like a large floppy ==> THESE indeed "format" the discs when a blank is installed, and this will reduce the capacity somewhat. Packet writers have the advantage that you can write multiple times without using multiple sessions (which DO add overhead in the form of additional lead-in and lead-out data). Nero's InCD; Roxio's DirectCD; etc. are common examples of these. Windows 7's built-in DVD writing capability also allows you to select a packet-writing format for DVDs (if you select to treat them "... like a USB flash drive ...".
Simply disable your packet-writing software and you'll be able to write a standard DVD with 4.38GB of data. [Or if you're using Windows 7's built-in writing feature select the 2nd option ("With a CD/DVD player")].
