+1 on the rant.
It's incredible that iTunes has this dictate.
Think about the film industry. What kind of effort goes into their previews, i.e. Trailers? Tons.
So let's say you're an unknown artist, with the greatest hit song ever written in the history of the known universe. Ambitious, yes, but let's think big here.
On your song, seconds 31-60 are the end of a long thematic intro into the first verse, which is a 1 and a half length verse. Too bad for you that starting at 61 seconds, you get to the pre-chorus and at 71 seconds land on the hook-of-doom that is the top of your smash-hit chorus.
All it would take is a little applet from Apple that would attach meta-data tags to the header of your AAC encode, before you sent it into your digital distributor. A little AAC encoder that had a graphic that is a fixed, 30 second ruler bar that you positioned wherever you wanted on your tune. Audition. Encode. Done.
It would be simple to set up the audition management software at iTunes to window that section, simply based on the meta-data tags that would be encoded into the file header.
In fact, since we have a direct arrangement with iTunes, I've just talked myself into making this a mini-crusade. It really is a good idea, even if I do say so myself, and just thought of it while reading this thread.