There are a few different factors to take into account regarding the sales of an Arcade game that could have an effect on its sales. It does goes past the 11,155 point you stated, so that's a good sign. The limitations of HDD space or lack of Xbox Live hinders a lot of people from being able to purchase it. A lot of kids underage also can't get access to MS points unless they buy the card from the store. The lack of 1000 achievement points or common prejudice against the purchasing of arcade games either because of a fear of being too short and limited in features or lack of physical data (having a disc and case) will deter people from buying it. Plus it's only been a few days. I'm sure a ton of people will pick it up as the month goes on.
These are all issues that BG&E2 wouldn't have. It'll be a full retail game with a shelf life and 1000 Gp to draw in players that wouldnt even normally play it (as sad as that is, at least it's financial support.) BG&E2 will, by default, do better than the original primarily for two reasons.
1. The hardcore fans that played the first either on the original consoles or the HD port and loved it enough to warrant a full-retail purchase of the sequel.
2. The achievement hunters, including our own X360A community, who will be after those 1000 Gp regardless (the one real saving grace of the existence of achievements IMO. It may support and encourage undeserving games like Movie Licensed trash, but it also gets more support for those little gems that otherwise would've been ignored)