The discussion so far on "Why so few?" DLLs seems pretty much on-target to me.
I would add: Ability to program a non-trivial DLL is a marketable skill that takes a long time to develop. There are certainly a number of fine examples of free contribution to the AB community in the DLL area (e.g. RMath, for one). One can only feel gratitude and appreciation for such "above and beyond" contributions. However, capable DLL authors have the same 24/7/365 limitations as everyone else, and must confront a simple choice about how/where to spend their time and effort: getting paid, or not getting paid. Since DLL writing is (almost) platform agnostic, DLL writers in the trading area will have a tendency to code for platforms that provide built-in support for locking a DLL to a customer or software ID. I would predict that such "commercializing" integration features would result in a distinct increase in the number of commercial DLLs available for AB.
