Why would I need a digital TV?

I was pleased to see Set-Top Boxes (STBs) for sale that would turn a display device into digital TV with recording capability. However, when I checked the manual for two prominent manufacturers' models, I found that neither was able to control the volume of its output. This is a disappointment, as it means that the display cannot easily be a monitor (because monitors don't typically come with remote volume control), so it effectively needs to be a TV, which contains its own tuner.

What's wrong with this? Let's address some possible arguments for doing it this way:

Monitors that have speakers don't typically have remote volume control. You need a TV for that. Such a monitor would not need to control the volume if the device driving it can do it, as is the case with all computers you connect to it.
Monitors don't typically have remote power control. You need a TV for that. Monitors go into stand-by mode when you switch off the signal to them. The signal is generated from the STB. The STB has control over this. The viewer has (remote) control over the STB!
With a TV, you'll be able to watch a third programme while the STB is recording two others, (assuming a typical set-up of having two tuners in the STB). If I wanted a third tuner, I'd want it in the STB! Access to the TV's tuner is probably through a different kind of interface; by keeping all tuners in the same box, there is only one interface to learn and use. What if I want to record three programmes at the same time? I don't want to use two interfaces to do that. Essentially, keeping a tuner in the TV repeats all the problems that existed with analogue TVs and VCRs; there is no excuse for that, now that it's all digital.
If you get a 3D TV, you'll be able to view 3D photos and watch 3D programmes. No. 3D display is a not a product of the tuner. A Sky STB can send 3D pictures to a 3D TV through its HDMI interface, by-passing the tuner, so a TV in such a configuration is only being used as monitor.
Ah but, what if the TV needs to interact with the viewer about whether to display a 3D image as flat? The STB can generate that message, and the viewer can interact with the STB.
With a DLNA-enabled TV, you'd be able to access your networked media storage. This is not a function of the TV's tuner; data comes in via the network port over standard networking protocols. The TV doesn't even have to have the functionality; put it in the STB where it belongs!

Essentially, there are no activities involving the TV that exploit its tuner, other than activities you'd use the STB for.

So, to those who design such household goods:

Ensure that there are monitors that:
- have speakers and accept audio input (e.g. through HDMI),
- can display 3D video, either by recognizing two half-width side-by-side images, or by alternating between two images at a high frame rate under control of the driving device.
Make your STB's volume output remotely controllable.
Make your STB's video output wake up the display and put it to sleep automatically.
Make your STB a DNLA client.

Now you have no need for programmable remote controls. There is just one remotely controlled device (the STB), and the display is just a dumb peripheral of it.

2019-11-05 update: The Humax FVP-5000T does control its own sound output, and so can be used effectively with a monitor. The documentation hints on page 5 that the volume buttons control the volume of your recorder.