Comment #24 on issue 2246 by [email protected]: beaming in 3/4 - a setting to not beam 3 eights against the beat.
http://code.google.com/p/lilypond/issues/detail?id=2246
I think that older engravings don't follow this rule because it wasn't until 20th century that composers began to actually stress music contrary to the metre.
In other words, i suppose the "don't beam against the beat" rule wasn't needed before 20th century because there was no ambiguity.
Personally, i find music with strict-to-the-beat-beaming easier to read.
