It's probably hard to get everyone to agree on the defaults, especially the width / line-length of content. I think it makes sense to default to no width constraint, zero padding rather than picking something arbitrary. I personally start with 1em padding whereas the author seems to prefer 2em, (or 1.5, or 2ch which is roughly 1em)
Browsers used to default to adding margin/padding automatically to documents (Quirks Mode), but modern html includes a doctype to use "Standards Mode" which is more sane.
At the same time it would be nice to default to sans-serif typeface and line-height around 1.5 but it starts getting arbitrary very quickly and it's nice to build on something that doesn't change over time.
Browsers used to default to adding margin/padding automatically to documents (Quirks Mode), but modern html includes a doctype to use "Standards Mode" which is more sane.
At the same time it would be nice to default to sans-serif typeface and line-height around 1.5 but it starts getting arbitrary very quickly and it's nice to build on something that doesn't change over time.