Ehm no, not really 
But yes you did add some details I left out.
The point I was trying to make is that when you expect a print to look as it on screen it can be a dissapointment if you don't take the CMYK conversion into account.
I was trying to be polite about it, but you brought out the rolly-eye guy so I'll be blunt.
You are oversimplifying the cause and some of your conclusions are just incorrect.
Silkscreening does have similar issues unless you use spot colors. And even then, you would have one heck of a time mixing them properly to perfectly match anything done 20 years ago.
The CMYK conversion is based entirely on a profile that is either based on an existing accepted standard (like SWOP Coated) or a custom profile based on the color gamut of your output device. If you are using Photoshop, you can go to Preferences>Color Settings>CMYK Setup. Play with the settings in there and you will see that you can freely alter the results of the RGB>CMYK conversion. This is all related to color gamut and calibration of what you see on the screen relative to what is created on the output device.
Most inkjet printers are considered RGB printers when using drivers under Windows. Even though the inks used are the primary CMYK, the drivers are calibrated for and expect to be handed RGB color values. On Windows machines, there is a certain amount of built in calibration through the use of color profiles. Anyone who has used a "universal" ink refill in their printer has probably noticed a color shift due to this. The ink isn't the problem, the driver/profile is. It expects the ink to have certain properties, but as it is manufactured to approximate the average of each manufacturers "blend", it doesn't match any of them perfectly.
In short, in a properly calibrated system, a large number of RGB colors can be accurately reproduced with CMYK inks. There's no such thing as perfect calibration and it is considered to be the "holy grail" of the printing industry. But you can get very close.
As stated before, the problem gets worse when different types of CMYK colors are used. There are pigmented inks, dyes of differing tonal qualities, waxes, resins, etc. Each having their own color gamut. Some will faithfully reproduce more RGB colors than others. Dyes generally perform the best, followed by pigmented inks, followed by waxes and resins.
Also, don't confuse large format printers with the kind you have sitting on your desk. While many of the modern ones use similar technology, they often use different types of drivers. Most, if not all large-format printers require special software/hardware to take full advantage of the printers capabilities. The Windows drivers included with these are usually supplied only as a stopgap to provide basic functionality.
As one can surmise, there is a huge margin for error here, but to say that CMYK cannot reproduce RGB colors is innacurate. But to say that it cannot reproduce
all RGB colors is a true statement.
Media is also important. If the media is very porous, expect much of the ink to be absorbed well below the surface, which will make it appear gray instead of black (per your example). Looking at a solid black image through a cloudy adhesive or a less than totally transparent substrate will give you exactly the same result. And even with both of these issues under control, a poorly calibrated system can cause the same kind of problem.
So the simple answer to your "question" is that there is no simple answer. There are many variables at play, and to chalk it up simply to CMYK conversion would be an incorrect assumption.
RandyT
*edit*
Lousy spelling....
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