there was never a "stop supporting JRE 1" campaign like there has been for successive versions of IE.
there isn't a "stop JRE 1" campaign but there's a good amount of "stop breaking stuff with your updates, sun".
working in helpdesk a couple years ago, we needed to keep specific versions of JRE for specific applications. if you ever needed to use two apps that required two different versions of JRE, well....good luck.
From my understanding this is always because the developers did something they know they shouldn't have, like access private unsupported features of a specific version of a Sun JVM. I've seen quite a bit of java code written and all of it could run on multiple versions of Java with no problem.