Firstly, saying 'a source close to Bethesda' is as close to saying 'I made it up based on unsubstatiated rumours' as you can get.
Especially when you factor in this part
A reliable source close to Bethesda Softworks, speaking on the condition of anonymity due to their not being authorized to discuss the matter with the press,
The oldest way of saying 'I made it up' Nobody is going to risk their job talking to some internet nobody about something they probably signed an NDA regarding.
Second, his math is waaaaay off.
has confirmed that there are four DLC expansions already in various stages of completion not including Dead Money, with two additional DLC being considered for a total of 8 expansions to the game over the next two years.
So, Dead Money + four more expansions + two more = eight in total? I think he'll find that 1+4+2=7.
edit: Also DLC released over the course of two years? By that time everyone will be busy with Skyrim and the prime DLC selling period will be long passed. The delays we've had so far haven't been that bad lol