I guess that the quoted part was written because of my previous message about the fact that using variables, assign them values and then use them in the same scope in the where clause will cause the server to do a table scan instead of seek operation. If I'm correct, then let be clearer about it. If you use a clustered index, then seek operation will be used. If you'll use an appropriate none clustered index that is also a covering index to this query, then you'll get seek operation. If you'll use none clustered index that is not covering, then most times you will get scan operation. In your example you had a table with one column and a clustered that is based on this column. Here is an example that is based on the code that you've added to your message:

CREATE TABLE dbo.SARGTest (

DT DATETIME NOT NULL, filler char(1) default ('a'));

GO

INSERT INTO dbo.SARGTest(DT)

SELECT TOP (1000000) DATEADD(DAY, CHECKSUM(NEWID())%10000, GETDATE())

FROM sys.objects

CROSS JOIN sys.objects as s2

CREATE INDEX CID_SARGTest_DT ON dbo.SARGTest(DT);

DECLARE @s-2 datetime

declare @E datetime

SET @s-2 = GETDATE()

SET @E = DATEADD(DAY, 1, GETDATE())

--Using the varibles cause table scan

SELECT *

FROM dbo.SARGTest

WHERE DT >= @s-2 AND DT < @E;

--Using the same values but without the varibles use a table seek

SELECT *

FROM dbo.SARGTest

where DT > GETDATE() AND DT < DATEADD(DAY, 1, GETDATE())

go

drop table SARGTest