This one is going to be tough...how do I say this without offending someone? Oh well...
Bottom line, some of the most touted bowyers I've ever heard of don't know much about strings or string materials. Some of the nicer, more expensive bows come with some pretty lousy strings. This has been my observation based on around 20 years of buying bows and paying attention at tournaments and rendevous from TX to PA.
Sometimes it seems to be about money...which I don't really understand. Why put a cheap string on a bow that's in the $1,000+ price range?
The greatest bowyer may not be the greatest shot, so if they can't shoot the difference they may think there isn't a diference.
There are tons of misconceptions floating around, so even if they do a little research on the 'net they are liable to get something that isn't right. Lots of folks still think "AMO" means "4 inches shorter for recurves, 3 inches shorter or longbows"...and lots of bows don't begin to follow AMO either. (AMO is 3" shorter, longbow or recurve)
I've tried contacting a few bowyers over the years over some of the more off the wall comments I've seen. The one I can remember who did reply said something along the lines of he wouldn't warranty one material, but would warranty 450+...it boiled down to the 450+ felt softer, so he thought it was a less "harsh" material. At the time (it's been years ago), 450+ had the least stretch of any material on the market--but it does feel soft.
Another problem is inventory. For the best results, you make a string to fit a particular draw weight and length...at least with most materials. Materials like 8190 and BCY-X are making that variable less important lately, but before these came out my goal was to make a string that was quiet, durable, didn't stretch or creep, but wasn't so overbuilt that it added vibration or hindered performance...and serving it so it gives the proper nock fit for a particular style nock. That can be a pain for a bowyer, especially if they don't make their own strings.
Lots don't make their own strings because they don't like to, and/or it's not a real money maker. Some shops have invested in machines to do it for them--you have to really be turning out some strings to pay for these machines, and the strings are "one size fits all" and from what I've seen...well, they will work but aren't something I'd keep.
Some bowyers I've known purposely sent out the cheapest string they could find, because they knew most of their customers would replace it anyway. Send an endless, they want flemish. Send black, they wan't brown. Send it served to fit Bohnning Classics, they shoot Marco. Etc. etc. etc. And some just don't care as long as it has a string.
Lastly, there are several benefits to a well made string. It will be quieter, have less vibration, stretch/creep less, be more durable, and usually give you better performance.
Chad