HDCP can also be implemented over DVI-D (but not if it's converted to an analog signal), but support of this by video card vendors is so scarce as to be non-existent. So, HDMI isn't actually required (it is technically possible to use DVI) but if this concerns you I'd look for a TV and video card with HDMI.
The downside is that your choice in HDMI equipped video cards is going to be extremely limited. I probably wouldn't worry much about that right now, actually, and just get a DVI equipped video card (but make SURE the TV has a HDMI input). The reason I wouldn't worry about it is:
HDCP is only required to view high-definition content (BluRay and HD-DVD) at full resolution if the content producer enabled a "flag" in the content called the "Image Constraint Token". Because of the current proliferation of TVs and players (including computers) which currently do not support HDCP, all of the MPAA studios have currently decided not to enable this extra layer of protection. Any current BluRay or HD-DVD title will play fine at full resolution even when using non-HDCP compliant analog connections (such as VGA and component).
Most industry watchers expect this not to last forever, however, exactly when the studios will be free to turn on the Image Constraint Token is still very much up in the air. One big problem for it is the XBox 360 and it's HD-DVD drive. The 360 does NOT support HDCP in it's current form (it only has analog outputs for high-def video), and millions of them have been sold. If HD-DVD ends up surviving, and a sufficient number of 360's are sold with HD-DVD drives, it could be very difficult for the studios to enable this feature (and therefore lock-out all the 360 owners) without a serious consumer backlash. That's assuming that Microsoft doesn't release a way to add-in HDCP/DVI or HDCP/HDMI support to existing 360 units, of course, but the analysis I've read suggests that this would be very difficult with the options built-in to the 360.
Either way, even if this does happen a few years down the line, you could always just buy a new video card then. By the time that happens, I'd guess that EVERY video card sold would support the needed tech, so your selection won't be so limited. And, of course, the video cards will be much better and cheaper (simply because of the product refresh cycle in the GPU business). So, just make sure your TV has a HDCP compliant HDMI port and don't worry so much about the video card for now, would be my recommendation.