Well the soundboard thing is crap ..... just an excuse to be placed among the many other loads of crap that I hear tuning customers tell me that some tuner told them.
Most of the time when a piano tuner tunes a piano low, it's because he's either lazy and wants to make some money and leave, or because he doesn't want to spend the sometimes considerable time it takes to make a customer understand why it's gonna take multiple tunings and possibly broken strings to get it up to pitch.
I always tune pianos to standard pitch period, unless the situation is such that there's no reason for the customer to spend the money.
Part of my job is to do the customer right, so if it's a little old lady that only plays hymns to herself once a week, why should she pay for pulling it up to pitch? For her it'd be a waste of money.
But I ALWAYS take the time to explain the whole thing to any customer that has a piano that's low, and if it's not very low ... I ALWAYS pull it up without even discussing it.
Thing is ...... if a piano's low enough, (say 1/4 step or more) then it will not hold that tuning very well and that can be difficult to make a non playing parent of a piano student understand ...... and if they don't understand and the piano goes out of tune very fast, and it will, then they think (and tell others) that you're a bad tuner.
For many tuners it's just easier to tune it where it is and get out.
But after 30 years of tuning I've gotten my schpiel fine tuned to where I can make any little old lady understand. But it usually ends up being a half hour to an hour of conversation and very many tuners don't care to do that.
Oh, and also there are a lot of crappy tuners out there.