Thanks, Bruce. Doesn't always work out, though.
My honest first thoughts are:
Grillgrate grates are easier to cook on and require less babysitting. That's that lazy, "crutch" thing that Larry has mentioned. Whether you conside that a help or something to be ashamed of, I will leave to each person's decision.
I was shocked at how much grease found its way into the drip pan in my Summit from cooking just three moderate-sized ribeyes. (The third one was an ugly cut and not worthy of being photographed!) Using Grillgrate grates, most of that grease is all incinerated above. In fact, the drip tray in my little 2-burner Silver A Skyline hardly ever had grease, just dried up stuff that would fall in or that I scraped down. In addition to the open flow from using regular - well really super nice - stainless grates, the upside of using porcelain-coated steel in the firebox is the rapid runoff the grease that drips down. Faster, I would say than stainless steel, and definitely faster than cast aluminum. It was a flawed firebox design, but it had its upside, too.
The way my Summit behaved is the way Weber intended all along. The brief flare-ups are what Weber felt gave their gas grills the ability to mimic charcoal grilled flavor. I have to say that these steaks definitely had more of that then when I used Grillgrate grates.