This came across as exceptionally harsh and you should consider re-wording it. However, in light of this particular sentence, let me give you some free education.
TFP is an indie studio working on one product right now. As per the dates given in their kickstarter, they are currently several YEARS behind schedule for both beta and final releases. They are implimenting things that were in the stretch goals as "post release" features.
As such, they should absolutely be focusing only on the one game. Future products shouldn't even be considered at this juncture. This is why people are getting annoyed, and probably also why they got annoyed over the prospect of DLC (for the record, I figured Joel was talking about new maps in regards to DLC, and I thought that was a fantastic idea).
You may want to consider that viewpoint and those facts (regarding the release date) as to why people are getting a little irritated when other products and DLC are mentioned.