Comment by Mikhail_Edoshin

Differences are supposed to convey information. E.g. a paragraph's first line is indented to indicate that this is a start of a paragraph. Differences in line width convey no useful information, so the are suppressed. Same goes for overall text height on a page, although this rule is broken more often.

Typesetters are known to be very specific about small details. E. g. tables are typeset with meticulous alignment rules. It may look superfluous, but it is not. The nature of the craft is that it has to be invisible unless you know where to look.