Seems right now that the fastest pickup truck is the SRT-10 Ram 1500 of the Jesel Brothers. So it gives hope to those with "bigger" trucks. No, you couldn't haul a refrigerator in it (not sure many SRT-10's were ever used as pickups anyhow), but it certainly is a full sized truck.
As a long time fan of the original American mini-trucks (Ranchero's and Elky's) I'll always consider them light-duty pickups.
While before my time, here's what I've been told by those who were around in the 40's and 50's (feel free to correct me):
Typical American families didn't have three cars, or two, the number was most often one. What you drove has always told something about who you are, and back then it was no different. If the family car was a pickup, you were a farmer, a construction worker, or a mechanic. Hence the great popularity of station wagons. If you didn't want everyone to think you were a common laborer, you drove a station wagon, not a pickup. Let's face it, if you showed up at your finacees(?) house to meet her parents, a station wagon means you are probably the boss of the construction site, not the apprentice. Or showing up to bid a job, ditto.
Remember TV ads for that Milton Bradley game "Mystery Date"? The "dud" card was flipped over and it was a good looking young man, BUT he wore overalls and had a shop rag and a wrench. The "winner" card was some guy in a suit, IIRC. Kind of a caste system where if you see grease or dirt you were a loser, and a pickup was a "dirty" automobile.
But there certainly was a need for a pickup that didn't scream "I'M A LOSER!!" to the world. Some of the smaller brands tried at first to just put a nicer cab on their pickup, and Chevy followed with the Cameo, but none were successful. Ford was the first to figure it out correctly, and released the Ranchero. Chevy saw the success, and followed with the El Camino. Both Spanish names? This was no accident, and no, they weren't trying to sell them to Mexicans. It was supposed to give you the image of the rich Spanish ranch owners, who still must oversea his holdings on his silver-studded steed wearing his finest garb. El Zorro crud.
Eventually families would start having two cars, so the pickup could reside hidden in the carport, and slowly the stigma of being a pickup loser dissolved. Both the Ranchero and Elky died from lack of sales, and that era is officially over. It never disappeared completely, hence why many feel the need to dress up their pickups like a Rose Parade float.
So to pretend an Elky or Ranchero is not a pickup denies us part of our American Automotive Heritage. Be proud my pickup brethern. We are the unwashed who have been redeemed!