If you think of a browser as "just this thing that renders the page", you're correct, it's basically irrelevant how it technically is implemented. However that

If you think of a browser as "just this thing that renders the page", you're correct, it's basically irrelevant how it technically is implemented. However that'd be a very poor view of what a browser is. A browser is the platform, the runtime if you will, that lets us build applications on the internet. The first browser was pretty much good at nothing but rendering bits of text, shortly followed by images, and it grew from there. Today browsers have a myriad of capabilities that make exciting applications on the internet possible, such as: CSS transitions, CSS animations, CSS gradients, CSS calc, html5, WebGL, Web Audio Data, media streaming data, video elements, audio elements, binary data handling, object URLs, zip URLs, binary data requesting, cross origin resources sharing, WebSockets, WebRTC, realtime video/audio capture/encoding/transmission/decoding/playback, and so forth. This are features of the "browser engine implementation". And not all browsers implement the same features. For instance take iOS safari which lacked the CSS capability for position:fixed and usable overflow:scroll handling until just about a year ago. All browsers in 1997 already implemented this flawlessly, and correctly. But for whatever reason, Apple didn't until more than a decade after the inception of that feature. Similarly other features aren't implemented, too numerous to list, save for the one that annoys me personally most, that is WebGL. A similar situation was evident on the desktop internet in the time period between 1998 and 2004, where Internet Explorer 6 ruled supreme. But other browsers (chiefly Firefox) offered a different implementation, and hence put Microsoft under pressure to improve internet explorer if they wish to stay relevant. The same kind of pressure cannot be exerted on Apples iOS browser, because you're forbidden from exercising it. This is bad for the Web, it's bad for me and it's bad for you. Unsurmountable barriers to competition are always bad for everybody, except the one building the barrier.