Is there a reason why the follow stylizes a button so it has rounded corners in an Android device, but shows a lozenge button shape in the iPhone?

HTML:
Code:
<input type='button' class='buttonFormat' value='Enlarge +4' onclick='changeSize4()'>
CSS:
Code:
input[type="button"] {
font-family:Helvetica, Arial, sans-serif; font-size:13px;
float:left;
border-radius: 5px;padding:0;margin:0;
height:45px;
text-align:center;
}