Paul,
I guess that Dapol are planning to sell their "Sound version" products direct to the modeller for one reason :
To increase their profit margins !!!
I hope I'm wrong.
If this proves to be the case, then this seems to be very unfair on all of the retailers, (Big or small),as they are the Guys that have helped build Dapol's market share in the world of model railways, and have also dealt with some quality issues from Dapol.
I understand your point about the N gauge R-t-r sound fitted locos being cheaper overall, but I doubt that Dapol are going to start to retail their sound fitted versions a lot cheaper.
My personal opinion is that it makes NO sense at all to buy a "factory fitted sound" loco, and to then have to put up with the possibly inferior sounds or speakers that they provide.
This could mean then having to pay out yet more money, on a "Re-blow" and/or a better speaker.
I therefore believe it is a better solution, to support your retailer, and buy your DCC ready Loco from them.
Then fit the sound chip and speaker(s) of your choice, the cost overall would be about the same.
That way you have something that you can have a control over, and can therefore be pleased with the end result, instead of maybe having to put up with the manufacturers choice, which could have been chosen with a budget / profit in mind