If you've ever seen a tribute band you'll know that no matter how accurate the impression, there's something missing.
You can buy the same guitars as your idols, wear the same skinny jeans and get your hair cut just so, but that doesn't make you Led Zeppelin, or U2, or even Dumpy's Rusty Nuts.
It's a bit like that with so-called iPad killers.
The Galaxy Tab looked like a contender, but it turned out to be clunky, laggy and unsure whether it wanted to be a phone, a tablet or both.
Next's cheapo tablet turned out to be – surprise! – a pile of crap.
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PC World dropped the Toshiba Folio because there were so many returns customers appeared to be renting, not buying.
JooJoo? Boo-hoo, more like.
Why is it so hard to make a credible iPad alternative?
You're doing it wrong
The short answer is that the manufacturers appear to be looking at the wrong things. They're like musicians who think buying a Gibson Les Paul will turn them into Jimmy Page, or that being a big gobby pain in the arse makes them Bono.
What makes the iPad special isn't the hardware. It's the software.
We've been through this already with the iPhone. Early attempts to copy it were disastrous, because the approach wasn't "let's sit down with a blank sheet of paper and work out what a touch-based operating system should do". It was "let's make our phone look like an iPhone".
That's exactly what's happening with tablets. Apple has spent years thinking about what tablets should do, and it's built an operating system from scratch to make the tablet experience as pleasant as possible. That's a lot of work – so why not just cobble something together instead?
The Next tablet is an extreme example of the problem. Do you think anyone at Next really believes that their 10" tablet is the "great alternative to your home computer" the blurb says it is? It's not even a great alternative to a bit of paper with 'TEH INTARNET' written on it.
Not up to scratch
But even the big-name kit isn't up to scratch. Google has said that Android isn't ready for tablets yet, but firms are chucking Android tablets out the door anyway.
Even Windows 7's biggest fans have to admit that stuffing a desktop operating system into an iPad-style form factor is just silly, but Windows 7 tablets are incoming. Toshiba's Folio disaster suggests that at least some tablets are being rushed to market with unseemly haste.
That's great news for Apple. If iPad killers are nothing of the sort, if we're being asked to believe that writing 'Seabiscuit' on the side of a donkey makes it a racehorse, then Windows and Android tablets' reputation will suffer.
It's better to keep your powder dry and build something awesome than ship something sub-standard. If rivals can learn anything from Apple, that's it.
Put it this way. Who would you rather see live – Led Zeppelin, or Lets Zeppelin?