So normally, I would throw some olive oil over any cooked pasta so each piece does not stick to one another. However, does this hinder the pasta from absorbing the sauce? In essence, does the sauce not stick to the pasta anymore?
If you have a sauce, there's really no need to first coat the pasta with oil. I find that if you cook pasta al dente, and blend it with sauce right away, there's rarely ever an issue with the pasta sticking together. There's no harm in adding the oil -- will just contribute some richness -- though liquids like broth or some of the pasta water work more effectively at keeping the pasta from sticking.
Yes, the sauce might slide off. To avoid sticky pasta, cook your pasta al dente in plenty of salted water in a big pot - crowded pasta will stick together. And save a bit of the pasta water, like Amanda says, as that will do the trick if you have some sticky pasta.
I'm in the UK and we have a lot of top Italian Chefs on our TV. They say to add a little of the pasta water back to the pasta after draining to stop it sticking. Certain pasta shapes suit different sauces. check out Theo Randall's new book 'Pasta' for delicious recipes.
Adding oil is totally not needed. Remember that when you cook pasta you should add it to the sauce and not vice versa. And as per a previous answer, if the sauce is too "tight" you can ladle in just a little pasta water to loosen it up. I use a chinese style spider to drain and scoop and transfer the pasta forms. In Italy the key is restraint when saucing---unlike Italian-American where it gets smothered.