Acer switch does come apart into two pieces so you can use the screen part as a tablet only. The picture doesn't show that.
Not the one I looked at. There were several models to choose from but none that converted into a Win 8.1 tablet. There was one there that came apart, but it was of no interest to me because it ran Win 8.1 when in notebook mode, and Android when in tablet mode. That was of no use to me... it had to be fully Win 8.1 or nothing.
As for the HP All-In-One, the one I looked at was a more expensive Intel version with a 3.0ghz quad core and 8gb of RAM. There are cheaper AMD models [and some Intel ones] that 'may' have interested me, but they had none of those in stock at the time so I couldn'e evaluate whether I'd get one or not.
As for the price, you have to remember that I'm speaking Aus dollars here, and right now the AUD$ is only buying 78 US cents... which would explain a part of the price difference, and thens there's the different pricing on the various models. Besides, we Aussies have always paid more, especially for PC tech, with high gov't duties and taxes being the first additions to the cost.