Clustered indexing is now must - why? Earlier,  there were non-conclusive to me debates / discussions on whether to (always) engage / avoid clustered indexes.

Well, I understood that they are to be used sometimes with proper + specific purposes and context.   

SQL Azure Database Clustered Index Requirement:  


  "SQL Azure does not support tables without clustered indexes. A table must have a clustered index. If a table is created without a clustered constraint, a clustered index must be created before an insert operation is allowed on the table"  


does not fit in the previous conclusions, rationale and explanations.

What is the rationale, that I have missed from prev explanations, of rigidly imposing ubiquity of clustered indexes without any exceptions?
Read Inside SQL Azure:


  SQL Azure provides logical databases
  for application data storage. In
  reality, each subscriber’s data is
  actually stored multiple times,
  replicated across three SQL Server
  databases that are distributed across
  three physical servers in a single
  data center. Many subscribers may
  share the same physical database.


Clustered keys are required so that the three replicas of your data can be kept in sync. W/o  a key, is impossible to know which rows were updated. Heaps (tables w/o a clustered index) have only physical 'keys' (fileid:pageid:slot) and since your 3 replicas of the logical database share physical database with other logical databases the physical address on one server has no meaning on the other replicas, hence heaps could not possibly be replicated.