I recall some people asking that same question about desktop PCs and laptops at one time -- why do I need a higher performance CPU and more memory if I'm just going to use it for web browsing and checking email? It was and still is a valid question, for PCs as well as for phones. There are lots of different kinds of users -- some are power users that run intensive apps, others not so much. If your phone is "just a phone" to you, then no, you don't need that much power.
I do not think Apple really spends any money on their marketing but samsung might spend huge amounts of money. In any case it is very important for the company to prove the product is going to be reliable and at the same time the service is guranteed.