Can't answer about the grill grates, but I have a Weber Genesis (with sear burner) and it is built like a tank. I have had it for about 1 year now and it has done everything I could want. I bought the griddle and have used that to blacken steaks, cook eggs, bacon, etc and I am satisfied with my purchase. I struggled long and hard as to what type of grill to buy, and settled on the Weber for its durability. But I must also add that it compliments my other cookers: I use the SRG for poultry, corn on the cob and potatoes; the smokers - Bradley, UDS, and DIY WSM - for ribs, brisket, butts and smoking sausage; the Weber for all my grilling.
So my opinion may be tainted by the other options I have. (But you can't beat it for durability.)