You get the ADAM from the little girls not the big daddy if I remember correctly, and in Skyrim you won't purchase shouts you get them by assembling words that you find on walls with dragon scripture, as far as I recall it hasn't been explicitly stated you get shouts from killing dragons. Only that you get some of the dragon's power when you kill one.
I'd say you're right, in Bioshock, ADAM, the stuff used to get new Plasmids, which were sort of like spells except explained as being the results of genetic engineering rather than actual magic, comes from Little Sisters, who you could choose to kill in order to "harvest" all their ADAM or save, which would give you less ADAM but would get you special rewards if you saved Little Sisters, it did not come from Big Daddies, you still needed to kill them to be able to harvest or save Little Sisters, because they protected them and would attempt to kill anyone who threatened them, but the source of Plasmids was not Big Daddies, they just protected the actual source. Now, in Skyrim, you actually absorb the souls of dragons to increase the strength of your shouts, from my understanding, and gaining new powers from defeating bosses is nothing new in games, in fact, if you expand it to just special rewards in general rather than just new or stronger abilities, than it's pretty standard in a lot of genres, including RPGs, where boss type fights often allow you to gain access to chests containing high quality items or something similar. And it sounds to me that you don't actually learn new shouts from killing dragons, nor do you "purchase" them, instead you find the words that compose shouts from draconic script on ancient walls and such, killing dragons just helps to make your shouts stronger.
While Todd does compare dragons to Big Daddies or the helicopters in Half-Life 2, he doesn't say they're inspired by them, he just means to say that they're powerful, sort of boss like enemies in the game, I think, drawing a comparison to enemies that fill a similar role in other games just gives players a clearer idea of what Bethesda is going for here.