Why do we include TTF files in font-face declaration?

Question

If we have the following font-face setup (generated from fontsquirrel.com)

@font-face {
  font-family: 'FrescoSansProNormal';
  src: url('frescosanspro-normal-webfont.eot');
  src: url('frescosanspro-normal-webfont.eot?#iefix') format('embedded-opentype'),
       url('frescosanspro-normal-webfont.woff') format('woff'),
       url('frescosanspro-normal-webfont.ttf') format('truetype'),
       url('frescosanspro-normal-webfont.svg#FrescoSansProNormal') format('svg');
  font-weight: normal;
  font-style: normal;
}

What browser instance are we covering by using the truetype format? Aren't all the browsers covered by the other 3 (woff, eot, svg)?

Answer 1

Older Android browsers (namely 2.1~2.3) can't render woff/eot/svg. see http://caniuse.com/#search=woff