So as most driveways aren't fenced in, and are part of the most direct path from the public area of a street or sidewalk, to the main entrance of the house means a law enforcement officer is not engaged in a search in that area.
Probably correct but it gets complicated and is very fact specific with some grey areas. By the same token, sometimes an "intrusion" into a curtilage is okay. For example, a police "knock and talk" is where the police come to the front door, knock, and then ask a few questions when the resident opens the door. There is implied consent for the officer to be there since members of the public are generally allowed to knock at someone's door -- think girl scouts selling cookies. But, if you put up a fence (and a closed gate) there is probably no implied permission.
An interesting case just out from the Supreme Court is Florida v. Jardines
where the majority said police can conduct a knock and talk but cannot bring a drug dog into the curtilage (porch) because there is no implied consent for entry by drug dogs. The opinion is at http://www.supremecourt.gov/opinions...1-564_5426.pdf