There is zero percent chance developers are wasting a second making sure their sites actually work cross platform if not for iOS (and iOS more moneyed user base).
2. IE stopped all development of useful UI or web standards features, meaning if you needed the compatibility you were stuck with a stagnant browser
3. Due to #2, of course web devs hands were tied when it comes to adopting things like HTML5, <video> tags etc. Users would have needed to switch between the two constantly — Firefox for cool new sites and IE for their bank, school, government, whatever.
I would posit that none of the above seems true about Chromium. They do continue developing it, they add new web standards the most aggressively of anyone, and it’s available on basically every platform except the one Apple bans it from. Mind you I don’t really want Google to own it, because they are way too damn big even without Chrome… but honestly it’s no IE situation.