The four downloadable content packs were huge hits for Gearbox, so expect more in the future.
When Gearbox's Randy Pitchford says that 'Borderlands' has the highest attach rate of any DLC ever on Xbox, he doesn't mean that it sold the most, but that it sold the most based on percentage. That is to say, a higher percentage of 'Borderlands' owners bought the DLC than any others.
This can, of course, be attributed to the general quality and overall experience of the 'Borderlands' expansions, lauded for being more than just map packs and offering a significant amount of content for gamers to play through.
Does this mean 'Borderlands 2' will have a huge amount of DLC in the works? You bet it does.