I have always done that, don't remember why or if it has alwasy been like that. For me it is not a problem, but you may think different ;-)
Alternatively you can create a separate summary worksheet in Excel with links to the columns/rows in the original worksheet you want to show, and then link from MindManager to the summary worksheet. This has the advantage that the links are dynamic and therefore you don't need to recopy the original sheet every time you change it.
I agree with Andrew though that MindManager should show the original spreadsheet range as it appears in Excel.