The grates do not have the same design - that I can assure you.
I would suggest that you ask Brad @ GrillGrates (a site sponsor here on LTBBQ ) to offer his explanation tho.
Hands down, far and away, 100 times out of 100 - I would buy the Weber and the Grill Grates...*IF* I have the budget. The Charbroil is less - but fairly, will not last as long without a lot of parts changing and at some point....that gets expensive.
The Weber will go for many years, then you can rest assured that parts will be available as you need them.