why limited number of apps

[stapler101]

I know nothing about what it takes to "write an app" but I do wonder why there are so few apps for the touch pro vs. the iphone.
I am particularly interested in an app called The Pilot Library (aviation info).
Can this be duplicated for the touch pro?
It appears to me that a dedicated site (business) must exist to sell and service this type of application. The Appbeacon is a site that has the Pilot's library for example.
Does any site like this exist for the touch pro?