For example, the Ford Shelby GT500 http://www.ford.com/cars/mustang/trim/shelbygt500/ is probably not even turning a profit for Ford, but when someone picks up an automotive magazine with an article about the car, it makes them more likely to buy the entry level Mustang at 40% of the cost, or any other Ford product.
The GT500 still shares a LOT with a production Mustang, and al the economies of scale that imparts. It's also producded in very high quantities, 5000+ yearly. They're making money or they wouldn't buiild that many.
I've heard it explained that halo cars help create brand loyalty with an instinctual response similar to "My dad can beat up your dad" fights on the schoolyard.
http://en.wikipedia.org/wiki/Halo_effect#Halo_effect_and_bra...
The idea is the customer thinks: "Look at this amazing product Nvidia is producing! They must have great engineers working on bleeding edge technology!".
Even if they don't buy the $3000 GPU, they now associate Nvidia with high quality GPUs which may influence them to buy Nvidia product in the future.
Because they made what I thought was a decent phone at the time, they sold some other gear as a result.
I am not sure that Apple has a halo product, but if they did, it would be the new mac pro. (regardless of how you feel about the new mac pro...)
Also it was announced 6 months prior to release, was often sold out after it's release, and completely unavailable in most countries until months or years after initial release.
It was very much a halo product (at release, less so over time).
In fact, I would probably consider it as one of the most successful halo products ever - as it not only cast it's halo over the entire Mac+iPod product line, but it eventually became the revenue driver of the entire company.
Disagreement on the definition, or poorly explained personal example?
(EDIT: now that I think about it, our first iPods were the halo product that made me discard old Apple biases that I was carrying from the 90s.)