On the other hand, you don't want thousands of people left with out-of-date versions of the sun JDK. Suppose that a critical vulnerability was found in the last version of the Sun JDK plugin that still had the DLJ? Would you then support removing it in a security update?

Leaving browser plugins that can't legally be upgraded laying around people's systems is a severe security flaw, so the decision to invasively remove it is definitely the best option.