Just a "Why is it" question

I have burnt DVD-+ and DVD-- & RW’s. I have three DVD’s and a PC. Some of these will work on different players and not the other’s. I get a DVD from Blockbuster and it will almost play up-side down in all my players. What are they doing different to make them play. They burn, we burn, and they get the results. Just wondering…thanks.

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 “minus“ 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 “plus” 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 “minus“ format. Because of this additional capacity, they are slightly more expensive than “minus“ discs.

ps I got it from