This might have been one (of many) considerations when changing to the new Macbook power connectors. With the current design, there is no point in pulling straight on the cord as you described. The user must pull to the side of the strain relief, which allows it to do its job.
Has anyone had these problems with the new magsafe connectors?
As for the design, I'm inclined to agree with squidbot and say that the thread is a load of crap. It paints a poor picture of ID at Apple. I might be able to believe it at other companys but in the glimpse I've gotten into the design process at different keynotes, I find it hard to believe ID is so aesthetically siloed nowadays.
I'm sure ID passed deemed it as some sort of acceptable level of strain.