Was wondering what makes the S-series (S80/90) keyboards differ from the Motif-series keyboards.

Yamaha introduces the S80 in 2000; and then, introduces the Motif in 2001.  Yamaha continued the S-series with the S90 and S70 as; as well as continuing with the multiple Motif-series keyboards.

Besides S-series keyboards not having a sequencer and sampling capability, what makes an S-series an S-Series and a Motif a Motif-series? Is it basically just totally different sample-sets? 

Also wondering if the S80 came-to-be as an alternate 88-note version of the EX5 (minus the AN board....for which you could add as a plug-in with the PLG150-AN card).  OR am I totally incorrect? Is the EX5 a completely different beast?

Thanks,