Podcasting's weakness?

I don't want to start or jump into a flame war and I'm sure someone somewhere has talked about this (I haven't seen it though), but I've been hearing about podcasts for a few weeks now, and while I was reading a few blogs by folks doing this, I noticed some complaining about going through their monthly bandwidth in a matter of days. Someone said Adam Curry is moving 40Gb of files a day off his server now.

Then I looked at the specs and it looks like it'll download everything in all the feeds you subscribe to. Isn't that a design flaw from the get go? Not everyone publishing their audio files has access to a monthly terabyte data transfer, and it seems like it could be prevented with preview tracks. Audio takes effort, time, and bandwidth for both the producer and the listener, and preview tracks seem like the way to eliminate the bandwidth problem.

Why not load up enclosures by default with 30 second previews? Think excerpts for blogs, thumbnails for huge images, or how the iTunes music store works today. You listen to a clip, and if you like something, you can flag it and download the rest on demand, or later in a queue (build software to make this easy).

Seems like it'd solve the bandwidth problem for most folks, as they could subscribe to more feeds and sample before downloading.