The AAC/.m4a codec used in iTunes

Hi everybody, I just want to ask a few questions about the AAC codec used in iTunes 7.
I have read on the page (http://www.apple.com/quicktime/technologies/aac/) that the iTunes AAC codec has been developed by Dolby Labs but what I would really like to know is does this codec actually evolve (like new implementations, improvements of quality)?
AAC has been around in iTunes since 2002 or 3 if I'm not mistaking - so is today's codec better than the one used back then or is it the same?
I couldn't find any related information about this in the Apple site. All I could read about an eventual 'evolution' of the iTunes AAC codec was on hydrogenaudio's forum dedicated to listening tests (periodically comparing various audio codecs). The only update on the Apple website (shown above) regarding aac I've noticed since 2002/early 2003 is that recently the link to www.aac-audio.com (which wasn't functional for quite a while anyway) has been removed.
I'm asking all this not just out of curiosity but also because throughout this year I've converted virtually all of my CD's in AAC 128 kbps using the iTunes/QuickTime 7 codec and I just wanted to know is it still the best codec around at 128 kbps.
PS.
I am aware that AAC is part of the Mpeg-4 audio specs and it has been ratified as such, what I really want to know is has there been any essential improvements made in the iTunes AAC codec since its adoption by Apple (algorithms, implementation, whatever) resulting in better sound quality (through increased compression efficiency)?
I have started a similar topic in the "iTunes for Apple" forum but only one user has replied to me this far.
I could also post links to the listening tests mentioned above where iTunes 6's AAC codec came in 6th place in the 128 kbps category earlier this year. (Hope it's not against this forum's policy.)
Any help on this would be really appreciated.

Thanks for your response mate. I've been out of town for a while so I couldn't post the links to the hearing tests (hope posting these links isn't against forum policy as well).
So here goes - this link is about the ABX/Listening Tests performed in april of 2006 @128 kbps (done with an iTunes 6.+ codec version, which came at 6th place)
http://www.soundexpert.info/coders128.jsp;jsessionid=JBBFLKCLGLAE
Here's the test @192 kbps (done in july 2006)
http://www.soundexpert.info/coders192.jsp
These tests are the reason I asked this question on the first place but anyway (I couldn't believe iTunes codec was rated on 6th place, after all it's made by Dolby, right?!!).
Here's hydrogenaudio's Listening Tests forum (where I took the links above from).
http://www.hydrogenaudio.org/forums/index.php?showforum=40&pruneday=100&sort_by=Z-A&sort_key=lastpost&topicfilter=all&st=0
Cheers

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Thanks for your response mate. I've been out of town for a while so I couldn't post the links to the hearing tests (hope posting these links isn't against forum policy as well).
So here goes - this link is about the ABX/Listening Tests performed in april of 2006 @128 kbps (done with an iTunes 6.+ codec version, which came at 6th place)
http://www.soundexpert.info/coders128.jsp;jsessionid=JBBFLKCLGLAE
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http://www.soundexpert.info/coders192.jsp
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Here's hydrogenaudio's Listening Tests forum (where I took the links above from).
http://www.hydrogenaudio.org/forums/index.php?showforum=40&pruneday=100&sort_by=Z-A&sort_key=lastpost&topicfilter=all&st=0
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