[reaperducer]

This one surprised me:

  Helvetica
  Win: 7.34%  Mac: 100%

I know Microsoft prefers Arial over Helvetica, so I guess I shouldn't be surprised. But I didn't expect macOS to adopt it so widely.

  Arial
  Win: 99.84%  Mac: 98.74%

Then again, the Mac was designed from day one for this sort of thing.

[bombcar]

I believe Helvetica has shipped with every Macintosh since the very first one.

[dhosek]

Not quite. The original sans font on the Mac was Geneva. It was only with the advent of the Laserwriter that Helvetica became a standard font on the Mac.

[tracker1]

If you're really targeting either, you're probably better off with the fallback sans-serif which is often one or the other based on the platform (historically, not 100% sure on current browsers). Arial displays slightly better on Windows, and Helvetica likewise with Mac.

[ascorbic]

It just means it's installed by default on all Macs, but not Windows