I'd argue that is a flawed analogy.
When you taste the ice cream, you get the full essence of it. All the subsequent bites will taste like that one. You know what you are getting.
When you hear a 30 second song clip or see a movie trailer, you get a selectively packaged subset of the full product. I have heard many clips and seen many trailers that are simply awesome, and then the actual song or movie ends up being terrible.
So the analogy would be better if you got to hear the song once for free, and then had to buy to own, which is kind of between the two extremes now (leech it or buy it unheard). Radio (traditional or internet-based) does a decent job of this now, but only for singles. There is still no way to try a whole album before buying unless you catch it on the headphones in Best Buy.
The trouble with movies is that generally you don't watch them many times. I can't really speak for everyone there, but I know I would be much more willing to pay for movies if I could get a good 720p copy of it for say $10-15. The reason I don't buy movies now is that I don't want a pile of DVDs in my tiny apartment. I could buy them, rip them, then resell them, but as I understand it, this is just as illegal as downloading them to begin with. So to summarize, give us some format options besides just a DVD that costs $23.