Yes, today's smart-phones can access the web, just like a desk-top 'puter. Agreed. Thus *theoretically*, you could do what you're saying from in-the-field. HOWEVER, in my experience, each county has a different layout system. They each have their nuances of where to click, blah blah. Also, maybe this isn't true any more these days, but at one time, some counties didn't even have an on-line ability yet. But that might have changed by now.
Anyhow, if this app. has standardized the navigation, then there's no need to A) learn the idiosyncrasies of multiple county's websites, and B) have to log in and out of multiple counties websites, when crossing a county line.
I haven't played with this one much, but I recall from trying some county assessor's sites, a few years ago, that it was difficult navigating. Hopefully this is smoother and faster.