I'm sure there are more such places but do they really tally up to an especially large amount of passengers going into/out of Manchester? I don't know the answer to that and I hazard a guess that you don't either.
Additionally, these places won't be served by HS2 come Phase 2b. So there will be three 400m trains per hour near exclusively serving the Manchester-London market. One might call at Birmingham Interchange but that's about it.
Liverpool, on the other hand, will get two 200m trains. These trains will continue to serve intermediate flows such as Stafford to London. Considering the city's slated to get 2tph in the near future and Phase 2b is going to be some years away, will that really be adequate? Are you sure, Neil?
Then there's Leeds. A city that currently has 2tph to London but will end up with 3tph, possibly some or all at 400m, complete with all the new infrastructure that comes with it. Leeds' London demand is much closer to Liverpool than Manchester, whilst its HS2 provision will be much closer to the latter.
Additionally, Liverpool's metropolitan area is significant in its own right. It's not massively smaller than Manchester's and is similar to Leeds/West Yorkshire's. Thus, I have no truck with the 'out on a limb' seaside town crap.
So is it not the case then, Neil, that perhaps, just perhaps, there's more than just demand for services at play here? As tbtc alluded to on another thread with regards to Sheffield's provision: maybe there's one rule for Whitehall's regional capitals and another for everyone else? If so, and I've long suspected it to be the case, then it's not acceptable and needs reappraising and not just in terms of HS2.