Back when sound modules were more common, it was normal that the module version of a synth was quite a bit cheaper than the keyboard version. Sometimes they would be nearly half the price. In some cases, features like on board sequencers were left off, or in the case of the Motif ES, sequencer, sampling, and fewer expansion options. The nice thing about the Sequential stuff is that there is no functional difference between the keyboard and modules, ever since the P12 (the module of that is still quite easy to navigate in spite of the reduced controls, however).