"The green line shows an idealized analog waveform -- a perfect digital square wave. No power supply and processing system can achieve this level of perfection."
Nor does it need to!
For one thing you're not going to see square waves THAT messed up unless the device is broken or your Oscilloscope probe is improperly compensated. Additionally you'll only see very slight not-perfectly-square rise times if you expand the scope's time base for measurement.
Regardless, those so-called "imperfections" in the source square wave are easily handled and "cleaned up" at the receiving end. If you look at the signal handling tolerances of most digital chips it's actually pretty broad. If the signals are within those tolerances you're fine. And in those more critical cases with longer distances for the digital signals to travel there are specialized devices called line-drivers and line-receivers.
Think about this. If digital signals weren't perfect or as perfect as they need to be, digital computers like your PC would literally crash. They're designed to crash rather than give you questionable results. How often does your digital device crash?
The article is mostly a load of B.S. to instill FUD into the audiophile mind usually to sell them something they don't need.
