It's not rocket science but it isn't an easy model to simply copy.
The majority of their pubs are freeholds, so they own the land the pub is on. Because they own not far short of 1,000 pubs, that pretty much all sell exactly the same beers, they buy in huge bulk, at a price not available to anybody else. They also sign very long term contracts with their suppliers, meaning even more saving. I think the other main thing in their favour is that they are very selective about where they open pubs. Whereas a lot of their competitors inherited a large network of pubs, many of which will have being struggling for years.
It's a great business model and I'm a big fan. But unless you've got the money to go out and buy 800 pubs, all in high demand areas, it's not really something you can replicate.
It would be a bit like buying a burger shop and planning on copying McDonald's business model.