I didn’t know until today, but I discovered this is something Lilypond does, hence the fonts coming with LP come in different versions named Cadence11, Cadence14, Cadence20 and so on (I noticed this but didn’t understand why). The lower numbers have thicker strokes.
As OCTO recommended, this is done both with the different fonts and via software: on the smaller staves it automatically use the thicker fonts and draws thicker lines (stems, stafflines and so on).
I didn’t examine the fonts directly nor tested on LP since I use Sibelius, but I read all this on LP documentation here: https://lilypond.org/doc/v2.18/Documentation/essay.pdf (page 6-7, “Optical sizing”).
And BTW, on the same page is said that ledger lines should be thicker than the staff lines: is there a consensus on this among professionals here?
EDIT: of course this has already been discussed on Notat.io: viewtopic.php?f=7&t=50
However, I think it would be great if the most prominent engraving applications would imitate LP. Still, the anount of work in making eight versions of the font seems daunting.