LOL @ SFthink. Everything has to be balls to the wall, pro-style or bust. Nobody drives new Bimmers because they've become to sluggish and luxury oriented. GIVE ME A RACE CAR!
Open plan kitchens are a response to the way people live. You can ask "why" all you want, but people congregate in the kitchen. I don't know why. Maybe it's the smell of the food. Maybe people are interested in what's for dinner. Maybe they want to spend time with the host. But that's just how it is - open plans and open kitchens are a reaction to the way people live. People didn't start congregating in kitchens because the kitchens were made that way. They weren't.
I just moved out of a house that did not have an open kitchen. There was a separate living room and a separate dining room. Where was everybody when I was preparing dinner? Up in my g*ddamned grill when I was making a mess and trying to plate dinner. Our kitchen wasn't made for it, and yet there everybody was.
These days it's not uncommon for two parents to be working. Nobody's been home all day in the pro kitchen whipping up a meal to serve in the formal dining room. Cooking and cleanup have to merge with homework and family time. Even dinner parties have morphed into something less formal than a sit-down dinner. Hence the open plan, where you can actually kill two birds with one stone.
We just renovated a historic home with an isolated butler's kitchen, and we had the option to maintain the floorplan exactly as-is. It would have meant tens of thousands of dollars in tax credits to preserve it perfectly. But I turned down that money to be able to integrate the cooking (most of which I do) and the cleaning (most of which my wife does) with our family time, and to be able to be a part of the dinner party, and to keep an eye on the tube or whatever while doing these tasks. It was a no-brainer to want to spend more time with my 3-year-old, which is why some of the "family" comments (from people with no families yet, go figure) are particularly puzzling.
Sure, there are drawbacks. Perhaps you sacrifice some of the ability to clean up properly after dressing and butchering the whole lambs you have been raising in your backyard. And it's true that it exposes some of the mess (hence the recent proliferation of butler's pantry/kitchens where much of the cleanup is obscured). But the tradeoffs and accommodations for modern living are obvious and desirable for all but a select few who, for whatever reasons, must maintain monastic devotion to their craft.