They stopped issuing security updates for Snow Leopard. I had to move on. XP was supported far longer.
XP was supported because it took Microsoft eight years to make an OS that truly improved upon XP, and even if Vista turned out to be better than it was, that's still five years after XP came out. Combine that with the fact that Windows holds a majority of the vast and inflexible corporate market, and it was imperative for MS to keep supporting XP.
Lion came out two years after SL, and if you didn't like Lion, then Mountain Lion came out three years after SL. Then Mavericks, and now, after five years, Yosemite. Considering that Mavericks and Yosemite are free and support between five and seven years of Macs depending on the model, there's no reason to not have moved on by now unless your machine can't support it. Complain all you want about how 10.7-10.10 will never be as good as 10.6, or whatever the SL holdouts claim, but for most people, it's their choice to be stuck in the past. And if Rosetta is still crucial for your daily usage patterns... it's
really time to move on.