There was a time when web sites had to support Internet Explorer 6.
There was a time when IE and most other browsers used different versions of Javascript and the document object model.
For all of Microsoft's flaws and questionable decisions, this decade has been much easier for web developers than the previous decade. We can now (mostly) design and code client-side to strict web standards and, while cross-browser testing is still due diligence, we can be more confident that our code will work across browsers and platforms. Microsoft has started making Internet Explorer and their newer browser, called "Edge", far more compatible with web standards.
Microsoft, I don't agree with some of the things you're doing with Windows 10 (and I plan to use Windows 7 for the foreseeable future), but you have taken steps to greatly improve the ability of web developers to concentrate on making good sites and reduce worry about cross-browser compatibility.
Hey, just to be clear, this isn't a reason to be lax with testing in all major browsers.
