I'm not trying to be a smartass.
I completely agree.
There's no way they could make the poke walker such a big part of beating the game like that, by making and HM obtainable through it.
In the case of you losing it, or having it break, you would never be able to complete the game.
But in you assuming, from reports, that the pikachu knows fly, you know no more than us.
I would say it was a valid argument.
...Well, by all reports, it's that the Pikachu knows Fly, not that there is a HM Fly to get in there, which wouldn't be put in the PokeWalker anyways (I don't imagine they're making the PokeWalker that compulsory at any rate). So there isn't much need for that argument to continue, really. *whistles*