What does "purchasers of a new tablet won’t ‘end up with a doorstop’" mean?

Washington Post (June 17) reports Barnes & Noble’s offer of tablet software update at a surprisingly cheap price under the title, “It’s official: Nook Tablets are now ridiculously cheap."

It says:

“(There are) rumors that the company might pull back on hardware in favor of selling content for other companies’ gadgets, and therefore (lots of folks) wonder if it’s holding a fire sale so it can exit the tablet market. Could be. But it’s also possible that B&N is trying to clear out its stock because it has new models in the works.

In either case, I don’t think people who buy a Nook HD or Nook HD+ are going to end up with a doorstop. Now that the tablets work with Google Play services, they’ll be useful no matter what Barnes & Noble ends up doing.”

I can’t pick the exact meaning of “end up with a doorstop.” "Doorstop" must be a metonym of something. I first took it for “doorstep.”

Does it mean a makeshift solution for sweeping out the company’s surplus inventory? Is this a set of phase? What does it mean?

The term doorstop refers to a door-stopping device, “Any device or object used to halt the motion of a door, as a large or heavy object, a wedge, or some piece of hardware”. Like the terms boat anchor (“something obsolete, useless, and cumbersome [whose only] use is to be thrown into the water as a boat mooring”) and brick (“(technology, slang) An electronic device, especially a heavy box-shaped one, that has become non-functional or obsolete”), doorstop can be used to refer to obsolete and useless equipment.

A doorstop is a weighted item that holds open a door. A common doorstop (in simpler times) was a brick.

The reference to electronic devices as doorstops signifies that they have no more functionality than a brick. In general, it refers to obsolescence - the previous functionality of the device is long since gone, and you might as well use it as a doorstop. This was more obvious when electronic devices weighed more than a few ounces.

An interesting related usage is the verb, to brick, which means to render an electronic device useless, so that an unauthorized user cannot access the sensitive information of the owner. This is accomplished through remote software that renders the device no better than a doorstop.

The phrase means that the item in question is a piece of useless junk, having no more value than, say, its weight. Not being heavy enough to be used as a doorstop, however, the Nook could be useful as a paper weight, another idiom for something of little or no value that simply prevents papers from being blown off your desk. For example:

"My Playstation is fried and would cost too much to fix. I use it now as a paper weight."

In this case, "doorstop" means "useless item".

A bit like when people say a terrible letter is "fuel for the fire".

I would say it is a form of sarcasm. To imply one would use a complex item for a simple (and perhaps degrading) purpose; one which is vastly different to why it was created and probably insult whoever made it.

I'm sure you get the idea by now, just thought I would add a more concise and direct answer which gets to the point on line 1.