It seems the OLPC project has started to get some success, but it is not clear whether this is due to the use of Windows over the Open Source equivalent. This is the one piece of information missing from the BBC News report. Certainly the use of XP makes the device much broader in interest.
I wonder though whether if the XO had a more standard Windows style interface, it would be more successful. I am not certain that XP makes it work better, but I am certain a more standard WIMP interface would.