The inheritor is legally entitled to the data on that device (as they would to any other intellectual properties like writings, patents and works of art created by the deceased)
That may be true, but I don't see how you giving someone your iPad creates an obligation on the part of a 3rd party to help you read it. If you're going to give someone your iPad after you die, give them the password, too. Maybe dear old mum is quite happy for them to have the physical device, but didn't want her children pawing through her digital life. Who is Apple to decide that?
Jokes aside here, Apple is just being a dick, which is really what we can expect from Apple.
Quite possibly. Were I Apple, I'd want to help out, but I also wouldn't want to set the precedent that you can call me up and ask me to unlock someone else's device and I'll do it. Now if you give me solid legal cover, like, oh, say...a court order, then absolutely I can help you out.