I am currently using the BeIronFit plan too, mainly as i do not have a clue as to what I should do without it - I would have just learned to swim bike and run the distance, and then to run 15 miles off the back of a 90 mile bike ride...probably not the best strategy. So the plan whilst generic gives me a guide as to the volumes, intensity and length of training required/advisable for the distance. I am, already (1 week in) changing things to suit me - cycling is my limiter so i am increasing the volume of that and i am already a relatively strong runner (plus its bloody cold outside) so i have reduced that. Also, i don't see there is any benefit to me in terms of endurance/fitness etc running for 15 or 30 mins in Z2. That would be warm up - anything less than 60mins in Z2 I don't feel there would be any benefit unless it is a recovery run/part of a brick. And swimming, well I am not yet capable fitness wise of swimming the 3k required in the plan for week 1, so i did as much of the session as I could until my arms lost power and i stopped. Oh and the pool has been closed too.
I guess in short, no a generic plan is not ideal, but it is (for the novice) a hell of a lot better than leaving it up to me to decide what and how much i should be doing. Particularly me, as I know the arse end of b*gger all.