Doing so would be similar to trying to count every car on a fast moving freeway with dozens of lanes.
Some cars make a constant route, every day.
You can count on them being on the freeway at some point. Others make one quick dash and are gone. Even those pages which remain are constantly shifted as their maintainers develop new organizational patterns for their sites. Deciding which search engine is best for you depends on a few factors. If you seek the broadest, most extensive array of sites online, you're more likely to be happy with an automated search engine.