Well, the case of Opera's Presto engine being forced to die in the past few years proved that the holy grail of everything being fine and dandy if browser engines and websites follow web standards is a big lie.
Opera is/was known for its standards support, .
Google Service Drops Support for Opera
https://news.ycombinator.com/item?id=4195298
G+ doesn't support Opera... why?
https://news.ycombinator.com/item?id=2738099
Gmail sometimes shows "Gmail too slow? Switch to Chrome, a faster browser." for Opera uses and a similar message shows up on Youtube Google Docs.
Chrome and Firefox started their own take on HTML beta and experimental features and led to a race of broken standard support.
Too many standards are half baked, and are implemented by some browser makers in a half baked manner and are frequently rolled back in an incompatible way, HTML5 storage being just one example.
From "Judgment Day Arrives: Opera Implements the CSS3 Webkit Prefix" http://www.sitepoint.com/opera-css3-webkit-prefix/
"In February 2012, we reported the minutes of W3C meeting where Mozilla, Opera and Microsoft discussed implementing -webkit prefixes in non-webkit browsers. The reason: some developers use only webkit prefixes — their sites look good in some browsers, but broken in others even when they offer the same level of CSS3 support. The issue is especially prevalent on mobile browsers and many developers fail to look beyond their high-end Apple or Android devices."
"Opera analyzed stylesheets from 10,000 popular websites to determine which CSS values/properties would receive -webkit aliases:"
Final result? A browser engine known for speed, leanness and standards support killed, because it couldn't keep up with the big browsers' incompatible beta standard support, and the number of websites that go for the latest and greatest and don't care one bit about standards support over cool features.
Take a look at this HN thread about a broken Google site and you see a lot of people defending non-standard HTML because it works on their choice of browser. https://news.ycombinator.com/item?id=4594913
These things are evidence of a currently broken web regardless of IE's involvement, with webkit being the new IE. And it actually explains how some of IE's features and bugs came about in the early 2000s resulted in pain for alternate browsers. Prime example of a great thing: XMLHTTPRequest was not part of a web standard.
Though Webkit is open source, I am a bit wary of Chrome's dominance as Google spends a ton of money to bundle it with everything and promote it at every chance over Firefox/Opera since they don't have to continue paying them hundreds of millions for being default and building a big moat for their search engine in the process against competing and future search engines.