Would not use VOD much anyway.
You'd be surprised, there is a ton of free VoD content out there arranged by channel. Go to the HDNet VoD and you can download concerts, older shows from HDNet, etc all free.
On the H24/HR24 there are 2 network interfaces, but only one can be active at a time. So when it powers up it first checks the Ethernet port for a valid connection -- if that connection doesn't go active it disables the Ethernet port and enables the internal DECA interface. It is important while the tech is there that
the Ethernet cable doesn't get plugged in to the H/HR24 -- trust me, this will save you a ton of grief and head scratching if you get an inexperienced tech.
If you use DECA, then you need to get the Internet adapter which is just another DECA module with a power supply. That will link the coax DECA network back to your home network so that the receivers can get out to the Internet.
DECA is only required for the install to be supported by DirecTV -- MRV will work over either connection, but obviously all the receivers need to be on the same network. For my install I ordered MRV without the Internet adapter and my HR24s were set up to connect via DECA. After the tech left I plugged in the Ethernet lines to both receivers and rebooted and both MRV and VoD works great.
If you're going to use Ethernet, to get good performance it cannot be wireless or powerline adapter connections. It has to be cat5 runs back to a switch; the LAN ports on a router will probably
not be sufficient as most off-the-shelf home routers don't incorporate an actual switch. Things like the WRT routers use a software process to move frames from port to port that can slow down based on other activities the router is performing.