? ... from BOL ...

"Statements that make a simple assignment always set the @@ROWCOUNT value to 1. No rows are sent to the client. Examples of these statements are: SET @local_variable, RETURN, READTEXT, and select without query statements such as SELECT GETDATE() or SELECT 'Generic Text'."

... and ..

"Statements such as USE, SET <option>, DEALLOCATE CURSOR, CLOSE CURSOR, BEGIN TRANSACTION or COMMIT TRANSACTION reset the ROWCOUNT value to 0."