Do I REALLY need to install DVI and 15 pin cable?

I am working on a family room and have been given conflicting or incomplete info regarding what cables to run from the receiver's location to the video display. It has been suggested by an installer that I only need S-video for this. I went ahead and added 5 RG-6 leads for component video. What am I going to miss if I don't add a DVI cable (are they all the same?) or a 15 pin mini-din cable (are they all the same?) I was led to believe that the pin locations were not standard. The walls are pretty closed up, but I may add them if the cost of the cable is not too high. Thanks for reading and I hope someone can answer my question.
If you don't have DVI, its going to be hard to support the "next" HDTV. DVI is a prerequisite for the content protection schemes that the content holders have insisted on; I think the take on is that DVI will eventually be the way content is transferred.
What the dvi is for-- is your content providers can at their will change the resolution of hi def material. You will only be able to view in 1080 if you have dvi. Most all the STB's don't have this yet. The content providers, for a couple of years now, have had the ability to "down-rez" any movie they choose. The chip they can control is in most all boxes that are now in use. It is more overkill. You can't copy 1080 from sat anyway without spending obscene amounts.---So you could only copy older movies OTA. There was the first HD vcr that could, but it was taken off the market quickly.
If you install electrical conduit from your source to your display you will give yourself many more options in the future without ripping out drywall. Plastic conduit will only run a couple of bucks and is fine unless you are in a very heavy RFI area. Run a couple of HD nylon strings through the conduit when you install it. You can then use the string to fish other cables.