I don't think the problem a lot of times is not that people are not watching the weather, or are not aware what the weather is doing, so much as predicting the weather is not an exact science. Can't tell you how often I have placed an order for next week where the forecast looked fine and then we had a blizzard or heat wave or something.
The only time I have had major losses was one shipment from a big hatchery during the summer when the box was "lost" for a day and the chicks arrived late... the weather was really hot, but I have gotten shipments when the weather was just as hot and they did fine. They actually replaced that shipment the next week and they were fine. While I think that whatever happened to the chicks during the time they were "lost" was the problem, there are only a few hatcheries I would order from in the summer now because of the USPS shipping routes and how fast I get the chicks. For example, with the insanity that is the USPS, I get shipments from Sandhill (500 miles away) in about 18 hours, from Mt Healthy (175 miles) and McMurray (700 miles) in two-three days. Which I think brings up another point, the route the chicks have to take to get to you is as important if not more important than the weather and the distance. I really don't know how you can figure that out for sure without trial and error... and then you hope the big hatcheries don't drop ship from somewhere else.
The other big problem is if you want in-demand breeds, you have to pre-order, especially in the spring when most people want to get chicks. I usually place my spring orders a good six months ahead of time so I know I have a good chance of getting what I want when I want it. I do have chicks delivered to my work PO Box, which is in the areas main PO, and have them held for pickup, that certainly helps with how well they do. Most bigger hatcheries will usually let you cancel or move orders on pretty short notice (maybe with some sort of penalty if short notice), but most smaller ones or private breeders are not going to be as able or willing to do that since they usually do not have other buyers lined up to take chicks right away.