Darth Vader was given obsolete technology for his suit, as can be seen in this question. It seems odd that he wouldn't have been given similar technology. Why was this done?
As you refer to the previous question, I'll refer to the previous answer. Darth Sidious no longer needed an incredibly strong and dangerous Jedi warrior to protect him from a large number of hostile Jedi, to usurp the Republic. He needed a henchman capable of being a major threat to "normal" people while posing a reduced threat to Sidious, slowing the normal Sith progression of Apprentice defeating Master.
Additionally, the style of the armor is based on Sith designs.
Could it be that General Grievous's suit would have diminished any abilities to use the Force? Vader's suit was made via Sith alchemy making it compatible with the midi-chlorians. Grievous's suit is almost entirely robotic apart from the brain, which was what gave the robot its advantage of sentient forethought and equilibrium.
"The suit was constructed using various methods of Sith alchemy which served to augment Vader's severely diminished physical strength and vitality."
The reason for the suit being downgraded was that Palpatine wanted to confine Vader in order to prevent Vader from becoming more powerful and overthrowing Palpatine. One zap of force lightning and Vader's suit is fried.
I would say that it was to keep Darth Vader as a force user. Anakin was insanely powerful in the force, whereas Darth Vader was still powerful, but his was a "Shadow of the Power that he once held." General Grievous' body was completely robotic, save for his heart and a few veins and nerves. Darth Vader's, in comparison, held as much of his organic tissue as possible. If he had Grievous' body, his connection to the force would have been all but non existent.