Like with so many other consumer goods, you pay for the brand name.
Weber grills are good. I like them. I would never buy one.
Why? Because what you're really paying for isn't the quality of the item, it's the nameplate and the customer service that goes with it. There are other grills out there, for 50% of the price of a Weber, that are just as good. They can be hard to find, and they require that you know something about grills, but they're out there.
If you put an $800 Weber next to a $250 Charbroil Home Depot special of the same size, you can see the differences pretty easily . The Weber has four metal wheels instead of two plastic ones and two fixed feet, and all four wheels can be locked. The lid is heavier and the hinges aren't wonky. The firebox is a single welded piece and doesn't flex when you twist the lid side to side. The shelves under the grill are solid, and the doors line up correctly and have magnetic latches. The exterior is made with a higher grade stainless steel, which won't rust in year two like most of the cheap grills will, or better yet is enameled (less pretty, more durable). There will be a large legible temperature gauge, and it will read correctly. Every burner will have it's own igniter, and the burner covers will be thick and heavy (this is the part that most often fails on old grills). It will come with a custom grill cover that fits correctly. The box will weigh a fucking ton and be a bitch to carry home.
Grills surfaces are something of an ongoing debate, but I have always preferred porcelain coated cast iron (what most Webers have) instead of the shiny stainless ones, which never stay looking nice and are harder to clean, and dont' hold heat as well. Similarly, I am firmly in the gas grill camp instead of the charcoal camp. If I want charcoal, I can cook on the ground. I don't smoke.
So if you're an aspiring grill nerd, you can learn about all of this stuff and then comparison shop until you find a well built grill at a reasonable price. Or, if you're pressed for time and flush with cash, you can just overpay for the Weber and be reasonably assured that you're getting a good product.
Every business is trying to make a competitive product at a competitive price. There are a lot of very fancy looking shitty grills out there these days, which look great and will need to be replaced in 3-5 years. I've owned several of those, and rusted them out. In the long term, it's usually more cost effective to pay twice as much for an item that will last three or four times as long. That does NOT mean you have to buy the brand name, though. Learn to recognize a quality product, not a brand name that claims to represent quality products.