The kind of stuff you're talking about basically comes down to licensing more official data. For a start, with EA around, the licences may not be available for purchase - EA may well already have them under exclusivity deals for their next title. Secondly, licensing content must be one of the most expensive single expenses in game development; Transmission & Codemasters would need to be confident that whatever DLC. The DLC would not be purchased by every single person that buys the basic game and so they'd have to factor this in and I reckon that would push the price above what most people are willing to pay.
That's even before we get onto the topic of whether they'd even consider making DLC. DLC is a way of generating further revenue from titles which aren't going to have a sequel for sometime, Fallout 3 being a fine example. At the end of the day, DLC is just downloadable expansion packs. They're quite often smaller in scope than the traditional expansion pack as the pricing is more flexible without the fixed overheads of producing discs & packaging and getting it onto store shelves (where the retailer then takes a cut). I appreciate some of you are going to point to Valve's free DLC for TF2 & L4D1, but Valve are the exception to a lot of rules in games development.
Why would Transmission spend time working on DLC when it's clear that they'll be looking to release a full blown sequel in the franchise when the Ashes are in Australia in the Winter of 2010-2011? Any additional content they are able to develop now can be included in that game to compel people to purchase next iteration of the series rather than tab on DLC to AC2009, which there are no guarantee's that the majority of players would purchase.
There is also the complication of delivering DLC over multiple platforms. Valve have found no way support the PS3 with such content and are still struggling to deal with Microsoft and data capacity issues with the TF2 updates on the X-Box 360.
Basically, I think this is a moot discussion. Let's just hope they give us a decent patch instead.