Two RG6 cables because a lot of people watch TV OTA in addition to their cable/satellite service. Two CAT6 cables -- 1 for network and the 2nd one for a home phone. If it's not used for a phone, there are 8 conductors that could be utilized for a wide variety of other things, including remote control of a DVD player located elsewhere in the house.
Most of the general public are not educated in these things, and don't think of 5 years down the road. When they start building a home, they go with the minimum cabling package, which often is 1coax and 1CAT6 to the master bedroom, and the same to a spot in the living room. Putting cables in other rooms costs more and is not needed. Some years later, they need a TV outlet and a network connection in a room they're going to use as a home office, so they cuss out the builder for not cabling that room and have to pay (more) to have it done. If the whole house is finished, they may end up with cables on the exterior, which nobody wants.
The safest route would be a conduit to each location where you think they may want cabling. If not that, pull in 2 RG6 and 2 CAT6 to each location (bedrooms, living room, family room). If they only want a TV there, stash the other cables behind the wallplate. Odds are that they will put a smart TV there and need a network connection, not wanting to do WiFi.