Subroman,
First off, Corel's documentation on their developer levels may be out of date. It reflects a program that was put into place during the development of Paradox 9, so I'd contact their sales office to see if it still exists.
Now, Paradox Runtime is a stripped down version of Paradox with some functions disabled. It's designed to let developers give Paradox functionality and applications to other users. Your users install Runtime and then install your application. As long as you're not doing anything that requires the disabled functions, everything works just like it does with native Paradox.
Because Corel chose not to create a separate SKU for Paradox v10, they dediced to include Runtime with WPO 2002/Pro. If you've upgraded to that version, then you already have a Runtime license. (In previous versions of the program, Runtime was always a separate purchase and ran somewhere between three to five times the cost of Paradox itself.)
Initially, Runtime v10 wasn't ready for the WPO install disks, so it was made available for download from Corel's web site.
Some developers do indeed require their customers to purchase at least one Paradox license, especially if there are a number of users at the client's site. This gives the developer a contact at the client's site for support purposes for things like table corruption, index regeneration, and so on.
It all depends on the price of your product and how many people you think will be using it.