Castle would probably prefer to stay with GeForce cards because they only have to modify an existing driver instead of forging a new one when changing to an updated card model. Why go Radeon when they can still purchase GeForces? Likewise for the high end cards: supporting the latest whiz-bang cards' featureset would be a sizable software-side financial investment which might only result in a meagre number of sales that wouldn't have otherwise happened.
A floppy drive + cable cost only about £7. Removing them from the 'Aria' is going to do little to cut the total cost of the unit or increase Castle's margin per unit. Then again, some people just hate floppy drives : )