I believe that subtitle is referring to, for example the iPod's dominance, where since its launch the only thing that competitors have managed to do is claw back scraps of market share to bring it down to 78%, from its high of 90%+ in the past.

Is the iPod unbeatable? Well, no, of course not. It's losing a sales, but mostly, from what I've seen, to smartphones, and of those, most are iPod Touches or iPhones. It's possible that soon, the iPod's sales will dwindle to minimal numbers, but it may still hold the majority of the market of MP3 players. Apple's MP3 player competitors didn't stand a chance, and the way things look they never will, not until something changes pretty dramatically in the market. That's the key issue.

The iPad isn't 'unbeatable'. Something better will come along eventually. My question is, is that 'something better' going to be from Apple's tablet competitors? Or from another Apple project that renders tablets in general obsolete for the majority?

I suppose a better title would be 'Apple's tablet competitors can't beat the iPad', which seems true to me until they change something to improve their chances.