I imaging that differences in the C library could affect the result as well. In fact, I'd say it's likely here since both numbers are the same, just with a different number of digits being printed.

Update: Confirmed

$x = ( -95.3009707988281 + -95.1877600585938 ) / 2;
$h = uc unpack 'H*', reverse pack 'd', $x;
printf("%s\n%.16e\n%s\n", $h, $x, $x);
[download]

gives

# MS cl, Windows, x86
C057CFA3AEE5258A
-9.5244365428710950e+001
-95.244365428711

# gcc, linux, x86
C057CFA3AEE5258A
-9.5244365428710950e+01
-95.2443654287109
[download]

The number is exactly the same, it's just the conversion to text by the C library that outputs a different number of digits.