As a membership pay site owner and content producer, I actually agree with you on this 100%. I always go though my photos after I do a shoot and choose the best looking photos. I mean, I do have pictures that resemble some of the others, but the reason why is so that the viewer can see the same position of the model, but from several different angles. That's just my particular style of shooting. But yeah, zip files are convenient, but they can also be a pain in the ass, because as you say, the viewer ends up getting an entire folder of pictures, where many of them were not even desired to be saved ...but came along with the mass download.
I also agree with EggMcMoofin. Monitors are constantly changing and are getting much larger, but as far as my photos, I have the original photos on my server, and can at anytime convert them over to be MUCH larger, but instead I choose to leave them at reasonable sizes. I remember back in the day, joining a few pay sites (way before I even stated shooting content) - I always hated when when the pictures were SIZED SO HUGE. I would have to scroll over half my screen just to view the entire picture. So yeah, for the time being, I have my pictures sized at 1600x1200. I know that isn't huge, but when you click them on a standard monitor, they fill up the screen just enough so that you do not have to scroll all the way over ...which I think is a pain in the ass for the surfer.
But again, I very well may end up sizing my photos even larger, but just have not done so quite yet.