[seemslegit]

This means they need to be aware of this issue in the first place and is yet another side concern to bear in mind, so yeah - externalized cost.

[true_religion]

The reader uses their own font with or without ligatures. There is no cost.

[seemslegit]

Not really, too often on the web it is the font decided by the author or an intermediary - the above page is case in point or they wouldn't have been able to demonstrate it as I have never explicitly opted-in to ligatures at any point.