I confirm 50% mode-s and ADS-B for Europe, in US, it's around 15% ads-d
It's pretty pointless bandying percentages around without saying what they are a percentage of.
Clearly 50% of "flights" don't have Mode S if you are including all takeoffs and landings by light aircraft, ULMs, gliders, military, etc, so you need to qualify what aircraft population you're talking about.
Similarly AirNav's unqualified assertion that "Usually in Europe 90% of the flights are ADS-B equipped" doesn't stand up to scrutiny.