Comment by the_duke

I don't know where they came up with the 73 million sites umber, but let's assume there are that many sites using font awesome.

Most sites are obscure, and rarely get any visitors at all. Maybe 10 a month, or none.

Popular sites that receive a lot of traffic are also visited very frequently by the same user, so the font will be in the cache.

In addition, plenty of sites use a CDN for fontawesome.

I guess that number is off by several orders of magnitude.