There are two versions of Studio Series Perceptor. You got the second version, which has a retooled chest and arms because someone at Hasbro wasn't satisfied with the accuracy of the first version. It was already fine, but they made it better, I guess.
I suspect they just wanted to make Ramhorn but they ran out of slots for new characters, but they had a remold slot, so they included him with Perceptor.
I suspect they just wanted to make Ramhorn but they ran out of slots for new characters, but they had a remold slot, so they included him with Perceptor.