I don't think the sprites have gone...but there does seem to be an increase in detail for things like grass and terrain. This will hit especially hard in the graphics department. I'm running BI with medium/high settings on the battlemap on a GF6800GT 256Mb and huge units. If I crank everything up to maximum, it does show.

Don't think it's the units that are making the difference...I think it's down to the prettier battlefields!