I don't understand what's the strategy with Forza. Your most accomplished exclusive, according to the media, and the company basically uses it as fodder in not one, but almost every bundle available in the market. It happens in most of Europe, too, not only in the UK.
If you already have the system, the reasonable choice is to go only after the game. But if you're about to buy an Xbox, and the game is that good/attractive, it's as if they're leaving money on the table by "gifting" that game in bundles, instead of waiting for people to buy it. They could put any other title in those packs, instead of a new release selling at 50/60€.
It seems to work because it's cheap, compared to other choices, but I doubt there is no better alternative.