I think a nod to Greensleaves to be found as easter eggs would have been a nice touch. I wouldn't have wanted to see it as an 'intro' song in every game... Seriously KQ4 probably had the best introduction music in the entire series, and it was original.
For that matter Greensleaves only appeared on certain versions of the KQ games as far as I know. KQ1 for example had at least two different intro music depending on the system it was played on.