I completely understand your frustration, a machine 5 years old should run anything. Especially considering the average lifespan of my Mac laptops is about 7 years. (Hell, all of them still work, even the Powerbook which ended up having the screen torn (metal hinges, not a good idea Apple, not a good idea ...)).
Anywho, the point being, I understand your frustration, and it's quite valid as well. But I do get Apple's argument. I'm not too savvy on the OS technical parts, but parts of what made Mountain Lion so nice for me, is the performance. Basically it's just Lion, but done right. Like 7 is basically Vista, but done right. Everything feels 20% faster, and for me, it's what it needed badly ... But doing that probably required them to drop support for those old 32bit components (correct me if I'm wrong). So at some point you have to make a choice.
But don't worry, you're not missing much by not upgrading to Mountain Lion, my 8 yr old white Macbook with a Core Duo 2 still runs Snow Leopard for exactly that reason ... (and runs it just fine)