rewrite of RECENTLY DEAD tuples

Hello list,

ATRewriteTable in tablecmds.c uses SnapshotNow to rewrite and thus
does not copy RECENTLY DEAD tuples. But copy_heap_data in cluster.c
uses SnapshotAny and copys RECENTLY DEAD tuples to the new heap
file.

I don't understand why it is not needed in the first case. In the
second case I guess that there may be still a transaction with an
older snapshot running which should be able to open the rewrited
table and see the older (RECENTLY DEAD) tuple. Why must a
transaction in the first case not be able to do so also?

Regards
Benjamin