Yes. The update hasn't been pulled. It happens when iTunes recognizes you have the update already, so to prevent you or anyone else, who has already bought the update, buying the update again, for the same iPod, accidentally, iTunes removes the button. I'm glad they've done this. I was originally charged 3 times for the January Software Update. I contacted iTunes, and they are refunding £26 of it. (Thankyou Steve!)
I think this is the reason they have implemented this. To avoid having to give out refunds or store credit.
Then again, I could be wrong.
R-Fly