We love home theaters so this is a fun question for us!
You can think of HDMI 1.4 as the successor to 1.3. Specifically, it adds 4 new features to your HDMI connection:
1) Higher resolution capabilities (allowing for Ultra High Definition 4K x 2K which is about 6x the resolution of 1080p)
2) Support for 3D video at 1080p with compatible Blu-Ray Players, Set-top Boxes, PCs and TVs.
3) Audio Return channel allowing audio from an HDMI 1.4 TV to be passed back to the receiver though the HDMI cable rather than having to run a separate audio cable to the TV
4) Ethernet link channel allowing all of your HDMI 1.4 devices to connect to the Internet though an existing HDMI cable provided that just one of your 1.4 devices is connected to the Internet via Ethernet or WiFi.
We hope that helps! Let us know if you still need some clarification!