I did a little search and this is the best that I can come up with. Dont know how true it is
The DVD-R/RW standard was developed by Pioneer, and is used primarily by Apple and Pioneer. These â€œminusâ€œ discs can only be written to in one layer on the discs surface. In addition, this format is supported by the DVD forum, but is in no way an industry standard. DVD-R/RW discs are cheaper than the â€œplusâ€ format.
The DVD+R/RW format is supported by Philips, Dell, Sony, HP, and Microsoft. These discs can be written to in multiple layers, giving them slightly better and more disc storage than the â€œminusâ€œ format. Because of this additional capacity, they are slightly more expensive than â€œminusâ€œ discs.
ps I got it from