Umm, because DVI/HDMI are for graphics, and mobos that don't support integrated graphics don't need graphics ports?
A more useful answer might be that, for now, there are two chipsets to support these CPUs. One assumes that you want to use the integrated graphics; the other assumes that you want to do more powerful stuff and will provide a graphics card. According to an article on some other hardware site,
The differences between P67 and H67 chipsets are quite logical. The first one is targeted for high-performance desktops, while the second one – for systems working with integrated graphics. So, H67 supports two independent monitor outs, but cannot split PCI Express x16 processor bus in two for a pair of graphics cards. Moreover, H67 is missing some enthusiast functionality: this chipset doesn’t support processor overclocking and doesn’t allow using anything faster than DDR3-1333 SDRAM.
Taking into account numerous user requests, Intel is going to add another chipset to their LGA1155 family called Z68. It is going to be a hybrid combining P67 and H67 functionality. It will allow using integrated graphics (like H67) and overclocking the CPU and memory (like P67). Z68 is scheduled to come out in Q2 2011.