You're right snow leopard has to be server, lion is possible as non-server.
It's been a while.
I do remember being pissed as snow supported some older software via Carbon(?) which was removed in lion and it wasn't virtualisable.
It was bigger than some Carbon apps. It was Rosetta being taken out of Lion 10.7 that killed all PowerPC apps.
Snow Leopard nuked Mac OS 9 Virtualization ability within the OS, killed PowerPC support for running the OS on PowerPC Mac hardware and in Lion 10.7, the big one, Resetta running any PowerPC built apps on Intel. But Apple was forced to do the later since their license with IBM expired and IBM wouldn't renew it. After this happened, Apple would not trust something so important to a third party licensed solution again. Hence why Apple is not depending on anyone for Intel to Arm support. They built it themselves, from what we know.
Back to Snow Leopard: Even though 10.6 was originally slated to support from G3 to Xeon (they even had some promo graphics made for it) and there is an internal beta build with PowerPC support that is online.
Now that we know what happened (many years after the fact), I can see how Apple made the decisions it did with Snow Leopard with Apple being Apple. They changed their course and just took it all out and started with a cleaner slate, along with rebuilding the entire Finder and many other apps in 64-bit. This also explains why the bugs were so bad in the early releases up until 10.6.3 (from memory) as well.
It ended up being a clean up release and only charging $30 instead of the full $129 like previous releases.
Oh the memories this brought back. It spelled the end of the PowerPC Mac support and we were forced to live with Leopard for years after that on the G3, G4 and G5's. Apps dropped PowerPC support very quickly after that, so us PowerPC users became an island unto ourselves. It has been that way ever since.
But it was also the last Mac OS to have a long development cycle and therefore is still one of the most favoured and stable Mac OS releases in recent memory. Pros, including myself, didn't move off of 10.6 until 10.9 Mavericks came out. It also goes along with one of the most stable hardware Apple produced (until the 2019 Mac Pro) and that was the Mac Pro 2010-2012. Snow Leopard Server is also the best way to run older apps in virtualization with hacks from Lion to bring in sound and can also run PowerPC apps.
I'll stop there.
As you can see, the current transition is smoother.
Edit: Corrected my post! Rosetta was killed in Lion, not Snow Leopard! Where was my brain? That is the whole reason 10.6 was so loved for so long and the main reason I use it for virtualization. 😂