Depends who you buy through, some of the websites (such as thetrainline.com) automatically request seat reservations even if you don't ask for them (and even if the service isn't going to provide them!) My seat reservation for my weekend train journey, London to Dorset on SW Trains, had no specific coach/seat assignemnt (it just had "Coach * Seat *" ) as the train didn't have any reservations on it.
I buy all of my tickets via eastcoast.co.uk (or wherever gner.co.uk now redirects to), regardless of destination or intended train line, because they are one of the few that still post them to you for free whilst others (such as thetrainline.com) charge for postage.
I buy all of my tickets via eastcoast.co.uk (or wherever gner.co.uk now redirects to), regardless of destination or intended train line, because they are one of the few that still post them to you for free whilst others (such as thetrainline.com) charge for postage.