That was a very good explanation.  As an aside, it took me a very long time to understand why ISO carried over from film to digital, and understanding that is critical understanding things discussed in this article.  But as I understand digital ISO today it works essential the same as film ISO worked, and results in the same thing--image quality, graininess or lack there-of or digital noise nowadays), and so it was a natural carryover from film.  As so the discussion of sensor size was short and right on point. 

While it may not affect me today as I am a hobbyist pure and simple, and my camera line doesn't even offer a full-frame sensor TTBOMK, and my photo budget considers $2500 a lot of money--if I were choosing I'd go full-frame because it would make my old film lenses once again the focal they are, with no "digital conversion" to allow for smaller sensors.  In truth I don't care and it doesn't matter with a TTL SLR as long as you can think in terms of what you are really getting as opposed to what the numbers are on the lens when you put a 35mm lens on a DSLR, but I suppose it bothers some people, especially people who work exclusively with DSLR lens and would find 35mm film lenses annoying to work with.  I suppose those people wouldn't mess much with film lenses anyway so I'm blathering on about nothing at this point.  I'm very good at that....