I think the first comment on the article has a decent explanation:
"How about differences in price elasticity?
We know that demand for big ticket items are very price-elastic, so they price those items very competitively. But, given that you're already in the store buying something, you may have inelastic demand for the peripherals that you didn't know you needed to buy (or, you didn't know that it wasn't included)."
People will drive to another store to save money on a television; they spend their effort comparing these prices. Once they're buying a television from a store, they're (usually) not going to then drive to another store to compare cable prices; they're going to buy the cable at the same store they buy the tv at.
"How about differences in price elasticity?
We know that demand for big ticket items are very price-elastic, so they price those items very competitively. But, given that you're already in the store buying something, you may have inelastic demand for the peripherals that you didn't know you needed to buy (or, you didn't know that it wasn't included)."
People will drive to another store to save money on a television; they spend their effort comparing these prices. Once they're buying a television from a store, they're (usually) not going to then drive to another store to compare cable prices; they're going to buy the cable at the same store they buy the tv at.