That's what I'm curious about... Is it an actual renewal or am I certifying in something new since it's a different version?
Technically both; it's not like your 10.8 certifications become invalid once 10.10 or 11 comes out; for those who use Mountain Lion and do not upgrade, your knowledge will be no less valid. That said, importance of that knowledge will fade over time. Anyway, back to your question, the recertification exam is a shortcut and more focuses on what has changed between systems rather than the stuff that has been the same for the last three or four versions of the curriculum. They call it a "renewal" because ACTC requires passing two tests ordinarily. With the "renewal" exam, rather that doing the Support Essentials and Server Essentials exams, you just do a combined exam that glosses over what changed since the last time you got ACTC certified in a version of OS X.
With the new certification process, there is no more renewal. Once you're certified, you're done for that product (10.8 server) but now I might have to do a new certification for 10.9 server.
You are confusing the ACMT process from the IT certifications; they are not the same. Yes, you get similar looking pieces of paper, but it is entirely different. Contrasting to how it was done before and much like the IT certifications, an ACMT certification is permanent, though the value of that certification is dependent on how many qualification exams you have taken for newer hardware. Whereas, the IT certifications are also permanent, but only applicable to the version of the OS that you're testing for. For example, I still have my ACTC 10.6. That certification is still valid; but it only certifies knowledge pertinent to 10.6. I just got my ACTC 10.8 too, and while there will be an ACTC 10.9 cert to prepare for, the ACTC 10.8 cert is still permanently valid and will never expire. Make sense? Right now, none of us are ACTC 10.9 certified because the material and exams aren't out yet. When it comes out, those of us with ACTC 10.8 certifications will be able to take the renewal exam rather than the Support Essentials and Server Essentials exams.
Also, for ACTC, I don't understand why I have to take the 10.8 Support exam again when I took it for my ACMT certification. It's the same test, different name. So many things that don't make sense to me any more.
It's a different test; I have my ACMT and I did the renewals each time there was one dating back to 10.5; I'm also a seasoned ACSP (the cert you get when you pass the "Support Essentials" exam that you are referring to) veteran having done them since 10.6 (though I did almost do 10.4). If you prepare for the Support Essentials exam, you'll pass the ACMT OS exam handily, but if you go into the Support Essentials exam with just enough to pass the ACMT OS exam, you'll probably fail as Support Essentials goes a bit beyond OS support basics.
My nearest training center is 6/7 hours away in NYC, so I have to take a long trip just to take the exam, so I don't want to drive that far if I don't need to.
I honestly don't know about ACTC as this will be my first time with a current ACTC (Support and Server Essentials exams) certification on the eve of a new ACTC certification, but I do know that with ACSP (Support Essentials exam only) certifications, if you get one, all subsequent ones thereafter can be taken online, and open-note/open-book as they'll e-mail you a code to be able to do it.