While it may be more believable, the sample sizes and methodologies behind the two sites appear to differ.

marketshare.hitslink.com lists that they track "approximately 160 million visitors per month" to "40,000 websites" [1][2]

statscounter.com lists that they track "15 billion page views per month" to "3 million+ global websites" [3]

This seems to imply that there is a bit of difference in which traffic is tracked by the two, and that statscounter.com is probably tracking a larger share of global traffic. I'd be hesitant to say that marketshare.hitslink.com is 'more believable' - perhaps it simply tracks a subset of websites more similar to your own?

In addition, with statscounter.com tracking page hits rather than 'unique visitors' as marketshare.hitsink.com does, it seems to imply that each Android user would use their web browser more heavily than each iOS user?

[1] http://marketshare.hitslink.com/mobile-methodology.aspx [2] http://marketshare.hitslink.com/faq.aspx#Methodology [3] http://gs.statcounter.com/faq#net-apps

EDIT: Indeed, filtering statscounter.com by USA market only gives figures very similar to marketshare.hitslink.com:

http://gs.statcounter.com/#mobile_os-US-monthly-201202-20130...

I'd argue that the global stats are far more important than the USA only ones, but you're free to disagree! And just to try and tie this back to the original point a bit: all of these stats are a very long way from 80%.