PHP Single Quote vs Double Quote

Got an interesting article from my friend fandi.
It goes something like this:

-------------------------------------------------------

function getmicrotime($t) {
list($usec, $sec) = explode(" ",$t);
return ((float)$usec + (float)$sec);
}

$start = microtime();
$a = array();
for($i=0;$i<100;$i++) {
array_push($a, "Aaron rules!");
}

$end = microtime();
$t1 = (getmicrotime($end) - getmicrotime($start));
echo "

double quotes: $t1
";

unset($a);

$start = microtime();
$b = array();
for($i=0;$i<100;$i++) {
     array_push($b, 'Aaron rules!');
}
$end = microtime();
$t2 = (getmicrotime($end) - getmicrotime($start));
$t3 = $t1-$t2;
echo "single quotes: $t2
difference...: $t3

";
?>

Results:

double quotes: 0.001505970954895
single quotes .: 0.00078308582305908
difference........: 0.00072288513183594

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Even a quote makes a difference? Surprised huh? me too!