iPod Touch availability lacking in the US Apple Store, pointing to a March refresh

It was reported that on the USA Apple Store, some of the iPod Touch models are lacking availability. Something a bit odd for a product that has been out for quite a while now.

It was noticed that some iPod model colour and memory variations were lacking availability until 1-2 weeks time. Could it be that Apple is no longer manufacturing these older models in time for a prominent refresh?