I have an iPhone 5 with iOS v6.1.3. I have had the same question and I was not able to disable the "Erase Data" because it was greyed out.
Just then I remembered that I had Exchange Mail Box configured on my phone. Once I deleted the Exchange MailBox I was able to turn off the "Erase Data" section.
Now the Erase Data section slider is not greyed out and data wouldn't get deleted if you enter passcode wrongly
Hope this helps!