While I totally agree that WP should be helping to lead the charge here, I don't thing plugin/theme developers should throw up their hands and say "not my job". As plugin & theme developers, we ARE making a difference. In one year, the percentage of sites running PHP 5.2-5.5 went from 60% of all WordPress sites down to 35%. That's a pretty incredible difference in a single year. Now, imagine what would happen if core WP actually joined the effort :)