It probably varies from place to place. It the small town I was brought up in, the Sunday service was - and still is, according to my mum - a real community thing. It's outdoors, non-denominational and very well attended, whereas a two minutes' silence during a normal work day can often end up pretty meaningless. We did observe it in the office, but the instant 11.02 came round, the phone was ringing again. When I worked in a public library, most of the time was spent not in quiet reflectiong, but silently miming to customers walking through the doors that they should be quiet.