I wish it were that simple. I need all three and occasionally even use Safari... I normally have ~15 browser pages open and 2 browsers. Way too many systems/platforms/extensions have been IE-Specific for many reasons and with embedded systems firmware in devices like printers, FAX machines, Cameras, other AV equipment, Routers, Switches, banking/vendor sites with Java, Active-X, etc...
There is *no* way all the vendors will reach back and "fix" their embedded web interfaces on old systems. (Would you? How far back?) Everything not currently for sale (2yr sales life) is considered "legacy" since there is no new revenue stream.
For many years IE was not perfect and was certainly buggy, but lest we forget, for the majority of the last 10 years, (yes we use/support equipment 5+ years old), the other browsers so popular today either did not exist (FF 2004, Chrome 2008), were not well standardized, lacked features, had integration limitations, were not installed on enough systems to be worth writing for, etc... (And still do...) 18 years ago Netscape had ~95% of a very much smaller market. 10 years after that, IE had about the same 90%+ percentage. Another 8 years and the trend is similar. IE is 25-50% depending and trending downward...
Firefox is only about 9 years old and Chrome is only about 5.
It would be awesome if there we only needed one browser, but I believe that will not happen soon... We are the tech-savvy bunch who are less likely to be put off by the various issues, the real numbers for the population are not so clear at all and are certainly no where near the 5% for this post.
Clearly Chrome is gaining the most in many uses and IE is the biggest loser across the board, but none are truly universal. IMHO, if it were not for the hostile guerilla-style marketing of usurping the users browser and search engines with nearly every downloaded utility/installer, IE would still rule the web due to the fact that Windows is still ~80-90% of the desktop/laptop market. Not that this is a good or bad, thing, just an observation. I do have less trouble with Chrome than IE
Try this for some interesting reading...