Why would people buy the $39 corded adapter vs. the $29 regular one?
Although the pricing is tough to swallow on either, I can see the use for the cable version vs just the small block type adapter. Think about the phone itself and what it would look like with both that adapter on it and then the fat end of the 30 pin cable. Essentially two connectors stacked on top of each other, sticking out the bottom of your phone. (Look at post #16 in this thread for an example) https://forums.macrumors.com/threads/1439406/
The cable allows you to have the new, much smaller connector coming out the bottom and have the two bulky 30 pin connectors (male/female) away from the phone.
But I repeat, the prices are silly (but fully expected)