There are a lot of devices on the market right now (especially mobile devices) with a Micro-HDMI or Mini-HDMI port and no VGA or D-Sub output. Most manufacturers of said devices sell a cable that looks something like this:

I have yet to find a cable like this that claims to work on a wide array of devices. In general, these cables claim to work with one specific device only.

The way these cables work, I think, is that analog VGA signals are sent from the HDMI port on the device. This should work for devices that have special hardware on the motherboard/GPU capable of driving this.

Is it the case that these cables have to be custom designed for each device? Or, is it rather that any device which possesses this special "signaling of analog VGA over the HDMI port" can be made to work with a cable that is physically compatible (i.e. the HDMI end plugs into the device and the VGA end accepts a VGA monitor cable)?

Note that I am not looking for a product recommendation, just a conceptual clarification on what exactly these devices are doing. Also, a few remarks:

• The cables like the one depicted here are not digital to analog converters. I know about these: they are expensive, and they are the ONLY solution if your device only outputs a digital signal and is incapable of driving analog VGA over the HDMI port.
• The cables like the one depicted here are not straight crossover cables from VGA to HDMI, either. The crossover cables are designed to send a digital HDMI signal over the VGA port's wires; that is, the wire protocol is HDMI (digital) but the physical pinout is the same as VGA, even though nothing analog is happening. Once again, this is not the behavior that, I believe, the devices which I'm talking about in this question are doing. The cabling and devices that this question is about transmit the analog VGA data over the HDMI port (the HDMI port is in the device outputting the data, and the VGA side is the monitor/projector).