[Avodah] shekein derech bnei melachim

[David Riceman]

The mishna in Berachos knows that we have until 3 hours to say morning 
Shma because that's when princes get up.  Nowadays there are whole 
groups of people who awake later than that: night shift workers and 
Bertie Wooster/Auntie Mame types, to name two groups.  So why is the 
normative halacha 3 hours rather than whatever local practice admits?

David Riceman