Hey Krishna,
not sure what to think about being your guinea pig for your temp table experiments 
Anyhow, my guess on the reason for the missing delete/update functions on the temp column tables is that this would require much more complex handling within the data structure.
As this is a column store table we can assume that the structure looks pretty much the same as for the persisted tables.
However, when all we need to support is adding new records or throwing them all away (think of update as DELETE and INSERT), then this is much simpler.
That's of course just my two cents.
- Lars