Read somewhere White Macbook Discontinued, and also can see any of them on Apple website . Why is that ?

Yes they are. I heard that Apple might not be gaining so much sales momentum from them and the cheapest Air is cannibalizing its sales (selling like pancakes). But Apple will still be selling them only thru educational institutions. Haven't tried this but they might still be in there if you click on the Education Discounts. Nevertheless, I'm sure there are still tons floating around in the stores, ebay, etc. if you really want one. Bad news is, we won't be seeing Sandy Bridge or refreshes on those machines.