Great question, thanks! Though it would be nice for a little explanation behind the results.

Considering that BOL states:

"The following operations cannot be performed on the model database:

•Setting the database or primary filegroup to READ_ONLY."

Which obviously isn't true, you can set it, it just doesn't propagate it to new DBs.

Though the first option for script 4 should be updated to say NewReadOnlyDB instead of TestA. (That is what gave it away for me.)