Starter = shareware version of the OS. To get a fully functionally OS may as well stick with WinXP professional, unless Microsoft pricing it at similar price with win7 Home Premium or professional.
“There is no need to wait for Windows 7. It is a goal of the Windows 7 release to minimize application compatibility for customers who have deployed Windows Vista since there was considerable kernel and device level innovation in Windows Vista. The Windows 7 release is expected to have only minor changes in these areas. Customers who are still using Windows XP when Windows 7 releases will have a similar application compatibility experience moving to Windows 7 as exists moving to Windows Vista from Windows XP.”
(the other way of saying above quote) "Stop using our old product and buy one of our new products. We need the money. Our stockholders are mad at us."
... Microsoft can’t have a one- (or two-) size fits all SKU plan because it has more than a billion customers worldwide running Windows. There are too many diverse needs to shoe-horn them all into two SKUs.