The old stylesheet used a rather large paragraph indent, 48 points. It also specified a small vertical space between paragraphs, 4.5–6.5 points. Stock LaTeX values for these sizes are 15 points and 0–1 points, respectively.
The style guide has nothing to say about either of these parameters, so the decision is fairly arbitrary. The author feels that the slightly larger inter-paragraph skip makes it easier to pick out paragraphs, and the larger indentation is necessary to make paragraphs stand out with the double-spaced body type. In the absence of further input, we will retain the old stylesheet's interparagraph skip, but the paragraph indent is a bit large, so we'll reduce it to half an inch.