a desktop application allows you a variety of options with respect to obtaining and consuming content. you can listen to content on the provider's webpage, sure, but it narrows your options greatly.

and sure, its not really that tough to discover new content online. something that helps you discover new purely podcasting content just helps to reduce the noise and makes proliferation of the medium easier for people who have a lower tolerance of technology and/or inconvenience. i can find the podcasts i want just fine. but i'm the current audience. you need to make it easier for soccer moms or grandfathers to find podcasts in order to break out of the current stagnation.