Hi!
I havent seen the 'guts'of the latest Yamaha keyboards,but the Rolands use custom made chips for sound generation,along with so called 'one chip controllers'for control functions.
As for Wersi (as an'expert') I can give you the following info.
In the DMS series of th 80's was a card rack with a '8 bit 68000 master procesor' controling up to 'slaves' each one producing 4x2 voice components.No custom made chips yet.D/A resolution was 12bit for first series and 16bit for the second series called 'CD intruments'.Sound mixing was done by another board a 'digitaly controlled analog mixer'.
The Pegasus/Livestyle system of the 90s was using an 'Inmos Trasnputer' as a the main controller -also used for the blueish touch screen-while sound generation was carried out with 5 custom Wersi VLSI chips.A Motorola DSP was doing the reverb+effects,while a separate board attached to a 2.5'' hard disk allowed for immediate (0 loading time!!) access to 1024 styles and 1024 midi sequences.Final D/A conversion is 20bits
The latest Wersi OAS (Open Art System:Abacus et all)uses a standard PC board with a Celeron Processor which is used as the main controller of the system :
Separate controllers scan the keyboard,user switches and volume drawbars and two DSP cards -each with 6 32bit AMD SHARC DSPs-for audio generation (including the drumsets)and processing.A separate Motorola 5630 series DSP board generates the organ sounds-that's called the OX7.All audio processing is done in 32 bits digital including 6x6 channel mixer and there is only one 24bit conerter at the end of the chain.Standard models now have 512MB RAM and 50GB disks.
Yes,its very stable,and it is updated very easy by loading the new version from a CD.