> a peculiarity of copyright law means that the actual shapes of the letters aren't actually protectable by copyright -- you can copy an existing font virtually 100%, tweak a thing or two, and legally call it your own.

IANAL but this is only true in some jurisdictions, primarily the US and Japan.

Also, I don’t think it’s quite that simple either. The actual type face may not be eligible for copyright, but the computer code describing the particular curves and hinting rules and etc. is. So I think you can’t just trivially copy a font and modify it and call it your own.