I think it comes down to what the passengers are willing to pay, or in this case, unwilling to pay, for a ticket. They want to pay the absolute lowest price!
For the longest time, the number one complaint of passengers was too little legroom, so airlines such as AA, pulled out seats and increased legroom, but lo and behold, most passengers were unwilling to pay a slightly higher price for this, so AA put the seats back in.
jetblue had pillows, blankets, free headsets, free TV, low change fees etc., etc, but even though the passengers appreciated this, they didn't appreciate the slightly higher fare this service cost. Hence, it was a no win situation, particularily in light of the run up in oil.
jetblue, like most other airlines, pulled pillows and blankets of the airplanes a while ago, but realizing, that some passengers might want to buy said, they offer the option of doing so. One can compared it to Starbucks, some people just want coffee, but some want frappalattecappusoywithatwistandfoam, so Starbuck sells it, but it sure cost more. Go to any airport and notice what people spend money on, 4.95 for a glossy magazine full of ads, no problem, the aforementioned frappalatte for 6 bucks, no problem, thow in a sad looking salad for 8, sure load me up, but three dollars more for an airline ticket, "are you frigging nuts, that is like highway robbery?" Even if that airline offered better service than some others.
So, jetblue offers you the opportunity to buy a nice pillow and blanket set for $7, plus you get a $5 gift certificate. Seems like a pretty reasonable proposition to me.