Take apart a surge protector and you'll understand. Most of them are garbage components inside unless you have a really high quality unit.
Computers and computer-like equipment (DVRs, etc.) are real sensitive to voltage irregularities and any problems with fluctuating current tends to wreak havoc on them whereas many other pieces of equipment are just fine.
I am aware of two ways that these can affect digital systems.
One way is for a power supply/conditioner to be too sensitive, as happens in the case for Monster. Some Monster products are either defective or too sensitive. When a satellite receiver changes backfeed voltage, the power unit detects this change in potential and attempts to compensate. When you check backfeed voltage while plugged into a correct source, a meter will typically read a steady voltage, either 13 or 18 volts, switching between the two with a "standard" cadence or rhythm.
Check the same receiver on one of the offending Monster power supplies and you will see it switching back and forth but it doesn't quite reach either value and it is not steady. It appears as if the two are fighting.
The other way is due to simple voltage and polarity fluctuations.
IDEALLY, digital is all or nothing. In REALITY, this isn't true. Voltage fluctuations and changes in polarity can and will cause errors in 1's and 0's, causing them to be incorrectly decoded.
In electronics, polarity doesn't seem to mean much except when it comes to digital equipment. With Directv receivers, one thing that they correctly taught (IMO) was that when hooking up a phone line that you should check that the polarity is correct. Polarity of a phone line does affect the operation of digital receivers.
And when checking the polarity of the average phone line, it's about 50% chance that it's hooked up correctly. As I understand it, the phone companies dont worry much about polarity anymore.