They are going to try and pull support for 10.6.8 Snow Leopard because Apple might not release security updates for the OS anymore. This limit would have to be programmed in by Riot, and this is not a compatibility issue created by Apple. This is a pretty awful situation as I know a lot of you guys still play on Snow Leopard. I can even still play on 10.6.8 if I boot from my external drive, which I used for testing purposes.
Given the state of the client, this looks like a cop out to me, as I have no idea what benefit Riot would receive from avoiding Snow Leopard other than slacking on client optimization. As I have said in the other thread, the older the system a program can run on, is a testament to said program's optimization. This is the first step away from more work of testing on the older systems.
I think Isto's post does a good job covering it.
Just to give some additional context that was lacking in the original post.
The two primary reasons are that there are VERY VERY few players still on Mac OSX 10.6.8 . Of these players, almost all can either upgrade to Mavericks for FREE or spend $20 to upgrade to Lion.
Upgrading for you means:
1) You'll get the latest drivers and the performance improvements + bug fixes that come with them.
2) We can upgrade from the 10.6.8 SDK to the 10.7.5 SDK. The 10.7.5 SDK supports a wider range of features and has several bug fixes.
3) Apple has stopped offering security updates for 10.6.8. This means your computer could become compromised. Think of this as additional account security for your LoL account if nothing else.
For us removing 10.6.8 support means being able to focus our resources(QA + Engineering) and energy on fewer configurations.
1) We've spent a good amount of time fixing 10.6.8 issues (and continue to spend time tracking down 10.6.8 specific issues)
2) To support 10.6.8 we have to use a very custom build. You can't even build for 10.6.8 without "hacking" around XCode anymore (as butter alluded to). Our custom build got even more crazy when we moved over to supporting the new C++11 standard.
3) Apple is much more aggressive about ending the life of their older operating systems. They can partly do this by offering free/cheap upgrades to newer operating systems
However, this idea that we're "changing it under your noses" is a bit disturbing. That wasn't the intention. Likely, it was just because Player Support generally uses the support forum to communicate to players. It might be an appropriate time to end this duality between the two support forums and just have a single support forum.