"Are they actually improving these strings or just changing the names for marketing?"
I don't know about the other company, but BCY is constantly working to improve, even though they dominate the industry--I think they supply something like 90-95%. They have all the big wheel contracts, but they still try to improve.
All HMPE is not made equal. Original FF was SK65 Dyneema. Dynaflight '97 is SK75 Dyneema. Dynaflight '10 was SK78 Dyneema. 8190 is SK90 Dyneema. Dyneema is a trade name for HMPE or UHMWPE, and considered to be one of the best. There are cheaper versions.
Anyhow, the higher the number, the higher the grade. 8190 is made from the most durable, lowest stretch/creep HMPE available.
Other materials are blended with Vectran. Vectran makes the materials more stable in high temps, but fuzzes up more. 452X and Trophy are great blended materials.
BCY already has plans to unveil an even better material at the 2014 ATA show. I'm tinkering wih it now.
I have a few sample spools of 8190 for serious string makers and bowyers to try out. If interested, send me a P.M.
Chad