There is a very big factor that the article missed - license fees.
A good chuck of that fee is goes to licensing. The guide software, guide data, DVR, VOD, etc. often have per-box licensing fees the provider has to pay.
The $250 also seams low to me. I’ve seen numbers in the $600-$900 range. Cable STBs are also much more expensive than IPTV devices because they have tunners, upstream modulators, MOCA (for whole home DVR), switched digital video, etc. vs a IPTV box that has an Ethernet port and basically just decodes mpeg4 multicast streams. The cost of STBs is one of the reasons MSOs like the idea of network based DVR.