A while ago I wrote this post about aggressive browser spitting, in which I blame ourselves for the fact that we still have to support ancient browsers. In that post I propose an aggressive approach to browser support: if your browser doesn’t understand the current web standards it’s the browser’s fault, not mine. The browser vendor should fix it, not me. This, of course, is very hard to sell to clients. But you can definitely use it in your personal projects.
Some discussions with Albert de Klein, Robert Jan Verkade and Wilfred Nas (among others) kept me thinking about this issue.
And if that doesn’t convince them, just tell them it will cost them money if they want more support. Lots.