Maple tends to lean a little brighter than Rosewood on tone... Or you could say that Rosewood is a little warmer in tone... Both are good, we sell a lot of maple, but probably a little more basses with Rosewood fingerboards. One is not better than the other, they are simply 2 different flavors.
It's like asking is chocolate better than vanilla.... Some will like chocolate, some will like vanilla...
It's not uncommon, rather it's more of the rule that the fingerboard and the neck are 2 separate pieces that are glued together. This makes manufacturing fingerboard options easier and also makes truss rod installation neat as you don't have to route the back of the neck and fill it in...
Hope that helps, peace!