This is what I wrote on the other thread:

LilyPond is an old music typesetting utility and its input language. Nowadays it competes against other inexpensive methods of input, often found easier to use, and a file format MusicXML that is much more sophisticated (being relieved of the burden of easy editability by a human user).

ABC, in contrast, was designed as a music definition language. Typesetting is considered secondary, thus (last time I checked) it does not cater for many details of layout. It is well suited for sharing tunes and simple arrangements on Mudcat. When I want perfect sheet music from an existing ABC source, I import it to my wysiwyg software via abc2xml for a "final" touch.

I understand Stanron's reply to agree with me.

The bar line symbol | in ABC obviously has the purpose of making the code easier to read by humans directly. The small price to pay is some extra work for the writer and the possibility of contradiction.

(BTW: MusicXML, though not meant to be read by humans, also allows for "bars" with wrong sums of note lengths; MuseScore is notorious for producing such errors and then complaining about them. LilyPond is even less foolproof. Expensive notation software typically has fewer bugs, since those found will be corrected more quickly, but real fools still manage to produce ambiguous notation with it.)