Do websites need to look exactly the same in every browser? Of course not.
It is vital that we and our clients accept that web pages cannot and will not render uniformly in all browsers. There's nothing wrong with using all the latest tricks supported by newer browsers, so long as we still allow users on older browsers/devices to access the basic content.
We therefore take a graded approach to browser and device support. "Support" does not mean that everybody gets the same thing, nor does it mean that people outside of the specific devices/versions ranges we mention will not be able to access the content. However we rationalise "support" to a specific list so that we can test effectively.
A useful summary for statements of work:
We develop frontend experiences against a browser support list. While we aim for similar results across modern "HTML5 browsers", owing to the natural variation of browser and device capabilities, the visual design and experience will differ between them. We will actively support and test Internet Explorer 9+ plus the latest stable versions of Firefox and Chrome (both Windows and Mac OS) and Safari (Mac OS).
We maintain a default testing list of browsers and mobile devices. Any additional requests beyond this and we need to factor additional time and complexity into our estimates.
By "support" we actually mean "we will test on this device or in this browser".
All functionality will work, content is readable, variations are minimal but acceptable.
Release cycles or Chrome, Firefox and Safari are so short that testing against all but the latest version is impractical. Chrome and Firefox auto-update so we test with the latest auto-updated stable version. Do not test with Canary/nightly releases.
Projects or products delivered are tested against latest stable version but we cannot ascertain the quality on further future browser version upgrades. It is deemed to be working fine against latest stable version at the time of release.
The mobile landscape is huge, so we test on the most common devices.
By default we do not test against these browsers, nor do we consider them during development. Supporting these may require significantly re-thinking our technical approach.
Graded browser and device support is even more important in a responsive world. It is vital that we communicate legacy support early on in a project's life to set expectations.
There are specific things that won't work in "HTML4" browsers: