If you look on the Roland UK site then the GW 8 is called a Workstation, and so comes under the Synths/Workstation products, whereas the Prelude is called an Arranger, and so comes under the Arranger section.
Basically in the UK (As far as Roland is concerned) if it doesn’t have speakers it’s a Workstation.
Most other manufactures now also seem to be following this practice.
IMO if it does what you want, who cares what it’s called

Bill