If Sony is wanting to meet their forcast of 13 million PS3's sold by March 2010, then why would they want to intentionally undership the system? If the system can't meet sales expectations (after the massive resurgence of the PS3) it will make the system look bad and might make it lose the foundation it's built.
Sony isn't intentionally undershipping it. They are trying to get out as many PS3's as possible.