"Cable Ready" TV Tuner Cards

Hi, I have a question that I'm hoping is not too stupid. I'll try to be to the point, and any insights would greatly be appreciated. I recently built a HTPC with a HDHomeRun external tuner card. In short, my HTPC runs Vista Ultimate w WMC, and I have Cox as my cable provider. Also, I'm located in San Diego, CA.

Question relates to the number of channels that I could or should receive through my HTPC. My scan results using HDHomeRun and/or WMC results in only 15 channels, all of which are standard local channels (CBS, ABC, FOX). I regularly receive 700+ channels through my set-top box and approximately 70+ channels with a wall coaxial cable connected directly to my Samsung LNT5271F. The Samsung had to scan the channels just like the HTPC's process.

I understand that there are differences between encrypted/unencrypted channels and between analog and digital cable signals. But why is my Samsung able to receive 70+ channels (including MTV, Discovery, A&E, History) with its built-in tuner while my HDHomeRun can barely receive 15 channels? I know that HDHomeRun only picks up digital channels, but there's still a big difference between the number of channels that I'm able to receive.

In essence, what's the main difference between a high-end PC Tuner Card and a built-in cable ready TV tuner (in this case, the built-in tuner that came with the 5271F)? Is there anything that I could buy in order for my HTPC to capture more channels (i.e. Hauppauge 1600/1800?)?

Here in Colorado, Comcast only broadcast's the local channels in the unencrypted digital format (because they are required to do so)-- so that you have to either rent a set top box or have a compatible device.

By a recent law (FCC, i think) --cable providers have to offer some type of digital converter card but I have not seen any devices that support it.

I would call Cox and find out your options