Hashem told Moshe at the opening of Parshas Bo that the makkos will be so great that the story of yitzias Mitzrayim will be something passed on and related to both children and grandchildren, "l'ma'an tisaper b'oznei bincha u'ben bincha." R' Leibele Eiger asks why the Torah goes out of its way here to emphasize not only children but grandchildren as well. When it comes to the mitzvah of Shabbos, but example, the Torah only mentions, "atah u'bincha," you and your children -- there is no added mitzvah to see that one's grandchildren observe Shabbos. When one's children grow up and have children of their own, they can take care of them -- children eventually become their own "atah" of the "atah u'bincha" of the next generation. Why here does the Torah go out of its way to add a responsibility for the third generation as well?
Rav Gifter (in Pirkei Torah) explains that the inclusion of grandchildren here hints to the nature of the mitzvah of sippur yetzias Mitzrayim. The gemara (Kiddushin) tells us that there are certain mitzvos that a father is obligated to do for his son, e.g. milah, pidyon haben, to teach him a parnasa (that's not too popular these days). The mitzvah of talmud Torah is unique in that it requires not only that a father teach his sons, but requires that he teach his grandsons as well. The Torah mentions the obligation to tell the story of yetzias Mitzrayim to grandchildren to convey that the mitzvah of sippur is itself part and parcel of the mitzvah of talmud torah -- the Torah commands us to engage in the talmud Torah of a particular sugya (yetzias Mitzrayim) on a particular night, leil haseder.
This idea helps explain why there is no birchas hamitzvah on the mitzvah of sippur or on the haggadah -- since sippur is a kiyum of talmud Torah, it is exempted by the birchas haTorah one recites in the morning.
Rav Gifter suggests that krias shema shares a similar geder. The Torah requires that we learn a particular parsha twice daily. There is no birchas hamitzvah on shema because again, krias shema is a kiyum of talmud torah of a specific parsha and is therefore exempted by birchas haTorah. (2 cents of mine: see the Sha'agas Arye siman 1.)
(Achronim discuss whether/how one can be yotzei sippur yetzias Mitzrayim through shome'a k'oneh. Does every person have to read every passage of the haggadah, or is listening to one reader enough? My first thought was that if the geder hamitzvah of sippur is one of talmud torah, the question is exacerbated. Surely there is no mitzvah in listening to someone else learn and having kavanah to be yotzei! But on second thought, maybe the question of shomea k'oneh is even easier to resolve now. There is a kiyum of talmud torah in just thinking about torah. If one person reads and everyone else is attentively listening and thinking about what is being said, even without saying the words themselves, isn't that talmud torah?)