iPod's Achilles Heel?

I don't think so. But it does make for an interesting set of speculations.

The crux: "What Apple has, then, is a subscription scheme for buying hardware - each device rapidly expires, and there is only one supplier providing a repeat purchase that's compatible with your iTunes Store purchases. What the music business wants is a subscription scheme for buying music. Somewhere, in the middle they may one day meet." Read the rest here.

I imagine that if there is a weakness it lies elsewhere.

Me? I am pretty happy with Rhapsody (the magic charm is it's convenience). I see no reason to switch to eMusic, join on to Apple, and have no interest at all in Microsoft's Zune.