Note: OMG, I just finished to write this post and I see that you replied with a link with pictures of a bad soldering job... Draw your own conclusions!!!
I didn't change it to reflect new informations:It may be a hint, or maybe not..
If the limit is implemented in hardware, I guess it would be easier to produce the same PCB for both the products and then let an underpaid chinese add the missing component. This would imply imperfections in the soldering job. Also, it would be difficult to solder inside the metal shield, so I guess that the component is outside them. Now take a look at this:
http://www.eevblog.com/images/DS1052E-ADCsupport2.jpgDo you see any solder imperfections? Maybe components from a clearly different batch?
I see two possible flux residues: on the chip in the middle-top, and on the chips in the far left.
-The chips in the left are probably TLC2274 (the most similar name I could find), quad op-amps.
The lower one has a place for a component connected to pin 7. It's the only not mounted component in all the section! (besides one resistor on the bottom right). Also, that pin is connected to another resistor. Maybe it's a matter of moving that part to the free place?
I don't think so.-The chip in the middle has a resistor connected to pin 12 and 13.
This resistor, the one below it, and the similar one on the right of the "3EM" transistor, are the only 3 components mounted in an imperfect way in this section of the board. Coincidence?
What do you all think?