if we pretend that vghcartzs numbers are accurate
I'll stop right here, because I flat out don't get this dismissal of VGChartz. Are they accurate to an exact reflection of how many units are sold? No, of course not. But do they give very accurate prediction models that vary due to sample selection? YES.
Anyone who says VGChartz pulls numbers out of their asses don't understand basic statistical polling. You know they don't actually ask every voter in the country when political polls are done, right? That only the smallest number of potential voters, who may or may not even go to the polls on Election Day, are asked questions that are VERY open to bias and slanting... and still political polls are often accurate to reflect voting behavior to a high degree of accuracy.
VGChartz uses methods more accurate and less prone to bias than that. And they should be viewed as that - a barometer of general trends, a canary in the coal mine. Couple that with the fact that they have a long reputation of being ballpark accurate for the vast majority of releases and it becomes silly to suggest that referencing is not a viable option. So yes... let's "pretend" VGChartz is accurate.
than DAI sold in 7 weeks more than DAO(their best selling game) in 12 months. Also DAO life-time sales were around 5 mln? And guess which one was longer in development?
DAO 
DAO had also boost in sales thanks to big expansion 5 months after release and dlc line-up for almost a year after launch.
So no single player dlc for DAI in next 6 months? Yep, it probably bombed/ undersold. But i bet there will be one in 2015 since ME4 doesnt come out until late 2016.
Okay... well, call me when DA:I announces an expansion, then. As it stands, they can barely manage to release a patch faster than once a month for even the most widespread of bugs. We'll see if they actually improve gameplay/UI, let alone make new game content for DLC or expansions.
Not to mention "story" was one of the most widely touted aspects of DA:O's strengths. It makes perfect sense for people to want to buy more products that continue said story. DA:I's story, on the other hand, has received tepid reception at best. Will people be willing to shell out more money for more content of that story? Will people buy new copies of the game for new content when the original can't stand on its own two legs?
You're making a lot of assumptions. You are looking at DA:O's unnaturally long shelf life when it seems much more likely to follow DA2's sharp decline and descent into the bargain bin. The game has negligible replay value compared to DA:O, has no mod support compared to DA:O, has overall negative fan reviews compared to DA:O and doesn't seem to have nearly the post-release support compared to DA:O.
