Looking at the official press site of SCEA, we noticed that the PS3 with the 20 gigabyte hard drive seemed to lack HDMI support. This seems to be confirmed by an offical press release from SCEA, which indicates via comparison between the two systems.

However, it also indicates that the 20 gigabyte system won't have Memory Stick, SD or Compact Flash reading capability or WiFi support.

PS3 IGN