http://www.digitimes.com/news/a20050616A4014.html
DVD-Rs, like every other plastic product, has got pricier to make because the raw material, oil, cost more to buy. For most products the actual cost of the plastic is such a tiny proprtion of the total cost, the price doesn't get passed on.
However the CD/DVD makers have been in a vicious(ish) price war, hence the dirt cheap prices. So oil rises is just an excuse to push up prices and start making money not breaking even.
Xrati, Refinery capacity would be OK, but for that Texan oil refinery blowing up. That and
all the refinerys have been running flat out for so long they're starting to break down. The US may have no plans for new refinerys, I don't honestly know, but other countries certainly do.