That is because the new table and its constraints, indexes, etc, although having the same name, are different objects (with different object-ids) as far as the server is concerned. So all dependent objects (with their compiled code still referencing the old object-ids) need a recompile to reference the new table. In many cases SQL-Server is smart enough to realize the dependent objects have disappeared and will try a recompile on first use, but this is not a fail-safe method (and I have seen in the past that objects get recompiled on each use after that, or not using the appropriate stats, degrading performance).

Marco