Bergerie1. I'd be very suprised if 80% was the figure; very few business jets or military aircraft transmit ADS-B and many airlines aircraft do not - e.g. some British Airways aircraft. I would suggest that the figure is closer to 60%. Obviously it is not mandatory in any EU airspace so I accept that many aircraft may have the capability.
I would be interested to know how ADS-B will better ground-based radar. ADS-B depends on the crew properly setting up the equipment and in my experience a significant number do not. I was watching a European airline B737 "landing" on Ascot Racecourse a day or two ago; in 30+ years of using ground-based radar I never saw a similar occurrence.