Your work is not in vain, it's not as if everyone is going to switch to Mountain Lion anyway, if we look at the poor adoption numbers of Lion. http://imgb.mp/ivu.jpg
A lot of that is because of the hardware that supported Snow Leopard that wasn't supported in Lion. I'm one of those. Contrary to popular belief, no not all and probably most Mac users do not replace their MacBooks every year or two. I will be using Snow Leopard until the hardware I have completely dies.
For more fun, let's look at the adoption numbers of Jelly Belly or whatever the Android crowd calls it these days. Let's not even open the can of worms that is Windows adoption rates.