just because the kerel is available does not mean apple does anything with it. They stop updating darwin a long time ago and only used part of it for their own uses.
Apple is a hypocritical company plain and simple. They are very closed and controlling.
I would recommend you read the post you quoted a little more closely.
I would be willing to bet good money Microsoft has done more with help Open source than Apple. Just unlike Apple they do not brag about it or even say much about it.
Lastly the kernal really does not mean much by itself. You need a lot of the closed source stuff to go with it.
The kernel is used in OS X. Of course it's updated. There are separate releases of the kernel for each version of OS X.
http://www.opensource.apple.com/
Click a version of OS X. Then do a find on the page for "xnu"
The source is needed to make extensions (drivers) and is important for developers that do things that require certain access to the kernel. For example. Transmit, the popular file transfer client, has a feature that lets you mount an sftp server as a "virtual" drive. This uses something called MacFUSE which is a kernel extension "kext"
http://code.google.com/p/macfuse/
I wouldn't expect normal users to know this, but now you do.
You also do not need the closed source stuff. You realize that a lot of the command line stuff is actually GNU software right? Open up terminal and type "bash --version" notice the "GNU bash" there? Oh yea.... not closed source.
You could technically use a linux distribution, and with a fair amount of alteration use the kernel from OS X with it. This again, isn't something that you will see people do. But that is exactly what OpenDarwin and PureDarwin are. They compile the kernel and match it with a distribution of software such as GNU and it's basically an operating system. On top of that you could run X11 and have Enlightenment or Gnome or KDE running.
As for reading the links i put up. I know what they are, otherwise I wouldn't have posted it.
Read the readme file
Table of contents:
A. How to build XNU
B. How to install a new header file from XNU
=============================================
A. How to build XNU:
1) Type: "make"
...
It is the kernel. Do you know what a kernel is? I'm guessing you have some vague idea but you really don't know what it is, which makes you sound like you're talking out your ass.
And just for proof of updating...
OS X 10.6.6 has a version of xnu-1504.9.26
While
OS X 10.6.5 has a version of xnu-1504.9.17
and
OS X 10.5.8 has a version of xnu-1228.15.4
Not sure about you... but major releases get major updates... 1228 to 1504 (as from 10.5.8 to 10.6.6) is a pretty big number difference, those are likely build numbers which would indicate major changes. Meanwhile, 1504.9.17 to 1504.9.26 (as from 10.6.5 to 10.6.6) would be a small number, thus indicating minor changes.
Meanwhile...
Webkit is open source and it's source is also readily available via
subversion.
Funny thing is Android uses webkit, and Blackberry is using Webkit... Oh... and so does Chrome... from Google...
I'd say Apple just contributed more to the world of open source with Webkit than Microsoft has ever contributed or thought of contributing.