Here is one possibility:
WITH
MEMBER [Measures].[Internet Sales diff] AS
(
[Delivery Date].[Calendar Year].CurrentMember
,[Measures].[Internet Sales Amount]
)
-
(
[Delivery Date].[Calendar Year].CurrentMember.Lag(1)
,[Measures].[Internet Sales Amount]
), format_string = '#,###,###,##0.00'
SELECT
NON EMPTY
{
[Measures].[Sales Amount]
,[Measures].[Total Product Cost]
,[Measures].[Internet Sales Amount]
,[Measures].[Internet Sales diff]
} ON COLUMNS
,NON EMPTY
{[Delivery Date].[Calendar Year].[Calendar Year].ALLMEMBERS}
DIMENSION PROPERTIES
MEMBER_CAPTION
,MEMBER_UNIQUE_NAME
ON ROWS
FROM [Adventure Works];
The result of the above is the following:

A percentage measure could then be added like this:
WITH
MEMBER [Measures].[Internet Sales diff] AS
(
[Delivery Date].[Calendar Year].CurrentMember
,[Measures].[Internet Sales Amount]
)
-
(
[Delivery Date].[Calendar Year].CurrentMember.Lag(1)
,[Measures].[Internet Sales Amount]
)
,format_string = '#,###,###,##0.00'
MEMBER [Measures].[Internet Sales diff %] AS
IIF
(
[Measures].[Internet Sales Amount] = 0
,null
,
[Measures].[Internet Sales diff]
/
(
[Delivery Date].[Calendar Year].CurrentMember.Lag(1)
,[Measures].[Internet Sales Amount]
)
)
,format_string = '#,###,###,##0.00%'
SELECT
NON EMPTY
{
[Measures].[Sales Amount]
,[Measures].[Total Product Cost]
,[Measures].[Internet Sales Amount]
,[Measures].[Internet Sales diff]
,[Measures].[Internet Sales diff %]
} ON COLUMNS
,NON EMPTY
{[Delivery Date].[Calendar Year].[Calendar Year].ALLMEMBERS}
DIMENSION PROPERTIES
MEMBER_CAPTION
,MEMBER_UNIQUE_NAME
ON ROWS
FROM [Adventure Works];
Results in this:

Here is a better approach using the parallelperiod
function:
WITH
MEMBER [Measures].[Internet Sales PrevYr] AS
IIF
(
[Measures].[Internet Sales Amount] = 0
,null
,(
[Measures].[Internet Sales Amount]
,ParallelPeriod
(
[Delivery Date].[Calendar Year].[Calendar Year]
,1
,[Delivery Date].[Calendar Year].CurrentMember
)
)
)
,format_string = '$#,###,###,##0.00'
MEMBER [Measures].[Internet Sales diff] AS
IIF
(
[Measures].[Internet Sales Amount] = 0
,null
,
[Measures].[Internet Sales Amount] - [Measures].[Internet Sales PrevYr]
)
,format_string = '$#,###,###,##0.00'
MEMBER [Measures].[Internet Sales diff %] AS
IIF
(
[Measures].[Internet Sales PrevYr] = 0
,null
,
[Measures].[Internet Sales diff] / [Measures].[Internet Sales PrevYr]
)
,format_string = '#,###,###,##0.00%'
SELECT
NON EMPTY
{
[Measures].[Internet Sales Amount]
,[Measures].[Internet Sales PrevYr]
,[Measures].[Internet Sales diff]
,[Measures].[Internet Sales diff %]
} ON COLUMNS
,NON EMPTY
{[Delivery Date].[Calendar Year].[Calendar Year].MEMBERS} ON ROWS
FROM [Adventure Works];
Results:
