That's how it's meant to be, delivery is stupidly expensive.
And pizza cost sod all to make, so they are still making profit.
And you can change two toppings with no charge on most pizza options without issue. It's when you add more or make more changes you generally get charged.
Why do they send some good offers out in the new year, must resist.
Delivery is in no way stupidly expensive, pizza places have a standard price, to catch out people who are stupid and increase profit margins, and they have deals for anyone who can put half a minute of effort finding and you get decent value pizza.
Its marketing, make every pizza £8, no one feels like they are getting a deal, it doesn't "feel" cheap, make every pizza £16 and have a deal that is running for only this week make all the pizza's £8. Suddenly it looks like great value and you think you have to get one this week as the deal won't be on next week.
You're right, the deal won't be on next week, for a day, then a new deal for £9 is pizza and a bottle of coke, the week after its £7.50 but with only one possible topping, etc, etc, etc, etc, etc........ forever.
Pizzahut have had the 50% off £40 spend and £10 off £25 order running almost non stop for about 5 years now. The dominos deal is usually along the lines of £10 for any size any toppings in london, delivery, and £8 for collected. £16 is just the price they get the odd great profit on when people are too daft to use the "deals" page of their website.