Speaking to Next-Gen, Xbox 360 group product manager Aaron Greenberg has expanded on the company statement about March's NPD figures - which showed that 360 gained a slight lead on PS3 for the month, saying that full supply of the Microsoft machine is the key to staying ahead in the months to come.
"We had a lot of shortages where you couldn't even find Xbox 360s on sale in January and February," he said. "That really impacted our ability to effectively market at retail in March. We had retailers pull a lot of circular ads, we weren't being featured in-store. We were on-shelf for most of the month, but the barn was sort of empty. Believe it not, those retail circulars do drive part of the sales. We didn't have that support in March, but we will have that in April and around the launch of Grand Theft Auto IV."
Plenty more through the link. Well worth a look.