It seems that Apple has made it difficult, if not impossible, to use anything earlier than 10.7 on machines that shipped with it installed, regardless of hardware spec. As I've no interest in the iPad/Phone 'experience', 10.6.8 is going to be where I sit until forced to do otherwise. Recently purchased a refurb 2010 27" iMac with the i7 chipset, however... the latest CPUs in the Mini that shipped with 10.6 are 2010 Core 2 Duos(seems 2010 saw the last of the 10.6 installed products). I keep a Mini on hand for emergency backup and it performs HTCP duties in the meantime. Picked up a '10 Server that I browbeat into accepting a client version of 10.6.8, which gives me two internal drives. I don't use a laptop that much and a '09 SSD Air works fine with SL. LR4 and all my other Apps work fast enough on these systems for my purposes, so will use them until such time new hardware forces my hand. And as Macs chug along for years, who knows what the hardware and software landscape will look like that far down the road.
This sort of situation has always been the case, and not just with Apple products. I keep an old IBM XP laptop due to having to use specific software for my repair business. I'm also working on getting a Nikon Coolscan V up and running and unfortunately the latest OS that seems to work reliably is 10.4, and have been tinkering with a G4 Cube to use as a dedicated machine for it. I haven't worked with Win 7, but have beaten my head against Wintel boxes enough as it is. From what I've seen watching people using it, it's plagued with many of the same things I find maddening with the earlier versions.