<input> doesn't inherit the font from <body>
Solution 1:
It does not inherit by default but you can set it to inherit with css
input, select, textarea, button{font-family:inherit;}
demo: http://jsfiddle.net/gaby/pEedc/1/
Solution 2:
Form items (inputs/textarea/etc) don't inherit font information. You'll need to set the font-family on those items.