Possibly because you are binding to 'form'. You might want to make the bind more specific like this:
<form id=myform action=/home>
<input name=a>
<input type=submit>
</form>
<script>
$(function() {
$('myform').bind('keypress', function(event) {
if (event.keyCode == 13) {
$('form').submit()
}
});
});
