This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
I presume you're asking why top-level classes can't be marked "protected"? In that case, I've two questions: 1) what does the "protected" modifier do for you when you use it for fields and methods of a class? 2) What would you expect would be the result of marking a top-level class "protected" in terms of its visibility? Does the idea still make sense?