So you have this table:

BEGIN
CREATE TABLE ATB
( ATBID INTEGER,
NAME VARCHAR (200),
SETUP TIMESTAMP NOT NULL DEFAULT CURRENT TIMESTAMP,
PRIMARY KEY (ATBID));
INSERT INTO ATB (ATBID,NAME) VALUES (1,'NAME1');
INSERT INTO ATB (ATBID,NAME) VALUES (2,null);
INSERT INTO ATB (ATBID,NAME) VALUES (3,'NAME3');
END

From Sybase Central if you right-click the second of the rows and "Generate > Insert Statement," you get this statement:

INSERT INTO "Owner"."ATB" ("ATBID","NAME","SETUP") 
VALUES(2,NULL,'2010-11-04 10:13:45.805')

However, if you do this instead:

begin
declare @UL long varchar;
unload select * from ATB where ATBID = 2 into variable @UL;
select @UL;
end

You get this as the contents of the variable:

2,,2010-11-04 10:13:45.805

I'm guessing that because the insert statement is obviously going to another table, NULL has to be spelled out, whereas the unload is more often going to a file such as .csv where it would not be beneficial to spell out null. I'm thinking a program reading a .csv such as Excel would treat the spelled out NULL as the text 'NULL' instead of the NULL value and that's not good.

However I think it should be an option on the unload statement similar to QUOTES OFF/ON where you could specify NULLS OFF/ON with the default being off, but if you wanted them you could have them.

EDIT to Answer Mark

My use case would be that each of our customers have the same basic table structure.

So Customer A called and asked me to set something up for them that involves records in 2 existing tables in a parent-child relationship like an invoice - invoice details, or a vendor - vendor details but more generic, like a template for them to reference.
I like what I setup for them and would like to be able to insert it on the fly for other customers now that I have it set up once. However, the ID will not necessarily be in line with Customer B's database so I have to edit some things.

I thought I would write a procedure that basically exported the information formatted as insert statements I could use on Customer B's system without edits for this thing I setup and any future things I setup.

Using lots of replaces and string edits and dynamic command creation I have it just about done, except for putting quotes around the Timestamps. As I was doing it I thought that my replace ,, with ,null, and then replace ,, with , could be avoided if there was an option for unloading with nulls.

I'm still kind of stuck on the timestamp quotes, but that's the last hurdle.