It's not a ploy or a gimmick on Dixons part. Naturally I won't say how/why I know, but the promotion *is* being honoured.
I'm certainly aware of a number of people (approximately 1.5%) who didn't receive their email because of delivery issues. Those are/were beyond the control of Dixons and they've been doing their best to put things right. But it takes time to process that volume of individuals on a case-by-case basis. I suggest you make sure your problems are logged with the call centre if you genuinely haven't received an email, or have lost your email and it will be sorted as soon as physically possible. If you're concerned nothing has happened, follow it up with the call centre. But my advice now when you speak to them would be to ask to be manually redeemed because that can be done.
Cheques are being printed early next week to try and get the maximum number of people in the first run, so don't fret that you haven't got yours yet - no-one has! But they are going out shortly.