If you have ever wondered...I have.
I'm now back with the dry with high curcumin from my Spice Merchant's pepper/cinnamon blend.(LINK)
If not grown at home, price of the fresh is a killer budget item.
I think the point to note is that powdered turmeric is fresh tumeric dried and powdered. I suspect the powdered stuff from grocery stores is really old. My powdered turmeric and the bought stuff are like two different foods.
Definitely with spices age matters -- especially if they are powdered. I keep my Turmeric powder in the fridge. and only grind up the whole seed or berry of my other spices as required.