Onus :
It would take a unique set of requirements for any of these devices to make sense, particularly compared to competition. With the possible exception of the ASRock unit, the price is outrageous. If you don't have room by your TV for a [much more powerful and versatile] mini-ITX system, for the difference in cost you can replace your TV stand or component rack instead.
These are essentially for gadget-freaks with more money than sense.
Aside from an enterprise space where they need a not-so-thin client and desk space is a premium, I'm with you. I just can't see the point of spending more than $650 on what is essentially a miniaturized home office PC. Unless you
really need the desktop real estate, if you're going over $500 for something like this, why not just get a mATX?
The one exception here is the Acer. Except for the lack of an optical drive, it's a rather complete machine for $430. If you needed a simple, easy machine for a child, grandparent, or other less tech-savvy person, this isn't a bad way to go. The lockdown firmware actually might be a benefit so they don't screw it up.
But that still leaves the question of what situation you'd want one of these boxes instead of a $500 laptop that includes the OS, display, hard drive, RAM, and possibly a more robust CPU. If you really need a bigger display than 15.6", get the laptop, buy a $120 monitor, and you're still under the cost of most of these devices.
MajinCry :
On the contrary, there are plenty of performance issues with old games when using new hardware. My 6670 and 7850 play NWN 1 piss-poorly with my 965 BE, por ejemplo.
Intel's IGPUs fare no better nor do NVidia's GPUs. Speaking from experience.
My experience has been that it's a game-by-game basis, and it's one of the reasons I keep my old machines laying around. I've successfully run titles as old as the original X-COM and Duke 3D and more recent things like Homeworld on my i7 + 6870. Most of the fixes have been specific to the game, not necessarily the hardware. Black & White had texture issues with my older 8800 at first, but a quick search and command line flag fixed that. Strangely I didn't see the issue on the 6870. KotOR and KoTOR 2 would cause thermal restarts on my older X1650 until I disabled the vertex buffering, and that was even a WinXP system of the same era as the game. I may reinstall NWN on my current box and see what happens.
But it's easier to pull out my old PIII Win98 box for retro gaming ( I've never successfully run FFVII on anything past DX7. ) Though I do realize that few people want to hold onto and store hardware that old. Hopefully my wife doesn't make me throw them out any time soon.