TV advertisers expect to hear a lot of big asks this year, but not so many small requests. When NBCUniversal opens the media industry’s annual “Upfront Week” Monday, it is likely to do so with talk of the 100 th anniversary of the NBC broadcast network and three different types of sports to offer on Sundays. And while the media company known for such series as “Law & Order” and “Saturday Night Live” will almost certainly nod to new programming, Madison Avenue wants NBC and its media rivals to go big before they go home to decide whether to put millions of advertising dollars into their coffers — or somewhere else entirely. With streaming video breaking down what were once broad TV audiences watching at once into smaller pockets of viewership, advertisers are on the hunt for properties that can still bring the big stuff. Companies that can’t offer it aren’t likely to fare well in the “upfront,” the annual marketplace during which U.S.…