It's up to GMs to decide whether or not they want to apply Improved Fiendish Sorcery's benefits to other appropriate bloodlines, though if I had to redevelop this feat, I would include the daemon bloodline in its description as well.
There's nothing stopping GMs from simply applying the benefits of fiendish sorcery to other appropriate bloodlines, and such a clarification really works better as a house rule than an official adjustment or errata.
There were several reasons fiendish sorcery wasn't simply extended to these other bloodlines in Blood of Fiends: First, it would be unbalancing, since it would make tieflings easily one of the best races to play as a sorcerer if their bonuses applied to too many bloodlines. Necessitating a feat expenditure helps balance this benefit. Second, since most tieflings on Golarion come from infernal or abyssal lineages, it makes sense that most tieflings receive bonuses to these bloodlines, while only tieflings who have learned to tap into their ancestral power (represented by the Improved Fiendish Sorcery feat) would gain access to such enhanced sorcerous power. Last, it would be odd to put such a far-reaching rule adjustment in this book, since it would have broad implications not originally taken into consideration with the development of the tiefling as a 0-Hit Die race, and would contradict numerous other books that contain the rule.