I wrote about this at my blog (<a href="http://www.pchristensen.com/blog/articles/a-closed-apple-platform-is-inevitable-but-temporary/" rel="nofollow">http://www.pchristensen.com/blog/articles/a-closed-apple-pla...</a>) but here's a quick recap.<p>Since technology advances faster than consumer demand, the differentiating factor for purchases changes over time.  First it's possibility, then power/flexibility, then price, then convenience/usability.  iPods and mp3 players got cheap enough that the usability of th iPod/iTunes Music Store became the deciding factor and there was no demand for undercutting it on price.<p>Also, the music use case is so well defined that there wasn't much room to compete on flexibility.  PCs have miles and miles of flexibility, but by defining the role of the iPad as music, movies, books, and games (basically media consumption), it might be staking out a territory where it can outperform everyone rather than compete with commodity devices.