The area is more pronounced and it is more substantial. I think substantial is a key. It will hold more heat when the cover is opened up than the wire version which is key to holding more even temps inside the grill. I usually place my meat mainly centered on the inside part with the venting when I use mine. But, yah, they closed areas would be a bit more like a griddle, I guess.
The flat style of SS grates will give you the durability and low maintenance of SS while preserving a lot of the heat retention that the CI grates have. But the wire style SS grates won't have the same heat retention.