Where on earth did you hear / read that? That's just not true. You can grill perfectly on a Weber 57cm both with the lid and without. I do it all the time, and when I was growing up my father did the same and his Weber is over 25 years old! Food cooks quicker and more evenly internally with the lid on, obviously, but you can sear, cook and grill however you like. It's all about how you set the coals up more than anything else! When I do large cuts of meat, the lid is always on, but for burgers and sausages, if I feel like standing by the fire attending the meat then the lid stays off, and if I fancy just sitting down for a bit to relax then the lid goes on.
I picked up my Genesis-310 a couple of months ago. I'm still not entirely sure if it's broken tbh. I literally can't cook anything with the lid up, I can put my hand an inch over the grill for a while and not have to remove it. It still reaches 500f with the lid down though and it's also webers "motto" not to cook with the lid up.
http://www.weber.com/weber-nation/blog/lookin-aint-cookin
We have an old saying here at Weber that is considered the golden rule in grilling. If you're lookin', you ain't cookin'. Every griller should live by this mantra and always remember it as a golden rule upon which great grillers are built.
So what does it mean? Simple, keep the lid closed when you are grilling. Grilling with the lid open is a bad habit which is done by amateur grillers. Weber grillers know the key to perfect back yard grilling is keeping the lid closed. Grilling with the lid closed is a very simple tip which many people overlook. If you are looking to raise the level of your grilling abilities this step is essential. By keeping the lid open the grill will lose heat and will cause your foods to be grilled longer. By keeping the lid closed you allow the Weber grill to do what it was designed to do, grill!!! By keeping the heat inside the grill, food will grill faster and be more flavorful.
I'm talking gas here obviously, coals are a totally different kettle of fish.

Great fun to get everyone involved too. Had mine for £130 from Argos and there's not a mark on it. Easy to clean by talking the ash drawer out and giving it a blast from the hose.

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