If the demand for touch panels increases then the manufacturers of touch panels will rejoice and expand their business thus increasing the supply. The real problem here is that RIM probably wants terms on touch panel production that are not all-too-inspiring to the manufacturers to warrant expansion. For example, Apple is confident that they will sell X units of iPads in 2011, Y units in 2012, and so on. So Apple prepays for what they need.
RIM is not as confident with their Playbook. They probably need contingencies in any long-term orders they place to ensure they can get out of buying touch panels they won't need. If these were 9.7-inch panels then the manufacturer could care less. Anything RIM walks away from, they can turn around and sell to Apple (very smart of HP). However, who is going to buy all those 7-inch panels if RIM's Playbook gets off to a false start? Samsung? Nope -- they make their own panels from what I have heard.
Supply and Demand.... When there is real demand for more touch panels from consumers than those being supplied to Apple for iPad then the manufacturers will expand their production and take advantage of the opportunity to increase profits. The real problem here is that RIM's attempt at media hype is not equivalent to real customer demand. The only tablet with a large amount of customer demand right now is the iPad. That is part of why I tend to believe that the "media tablet" category is a figment of the imagination for market analysts. Market analysts assign a level of demand to the "media tablet" category and make projections, but the difference between the "iPad" category and the rest of the "non-iPad media tablets" is staggering. The iPad category is flourishing, the "non-iPad media tablet" category is a fledgling state at best (if not failing).
If not for Apple's success with the iPad how many manufacturers would have already thrown in the towel with "media tablets" and once again written it off as "the technology for tablets is just not there yet for mass consumption". Tablets failed in various forms for over a decade. iPad is the first and only mass market success in this area. If not for Apple, there would be no such thing as "Honeycomb" or HP Touch Pad or Playbook -- these guys are hoping they can figure out what Apple did right and find some way to ride the same wave the iPad is on -- while technical specifications are there, they have not yet figured out the "magic" of iPad -- ease of use, awesome software market, and the emotional response Apple manages to evoke with their user experience. Just a few examples of emotional response.... There is something delightful about pinching a stack of photos to spread them out across the screen or the way Apple's tiled app icons and folders gets adults to collect apps the same way their kids collect trading cards -- these are very emotional things that Apple seems to understand.