First of all, I don't really think people have any greater motivation "to upgrade Windows/Mac versions": Here are the usage share of web client operating systems (August 2010): Windows XP (48.32%), Windows 7 (19.81%), Windows Vista (18.43%), Mac OS X (6.42%), iOS (iPhone) (1.40%), Linux (1.34%). So nearly 50% are using an outdated OS (XP).
By contrast, here are the usage share statistics for browsers: Overall- IE (31.1 %), FF (45.1%), Chrome (17.3%), Safari (3.7%), Opera (2.2%). Breaking down IE by version- IE9 (0.2%), IE8 (17.3%), IE 7 (8.0 %), IE6 (5.6%). And for Firefox- FF4 (0.8%), FF3.6 (35.3%), FF3.5 (5.6%), FF3.0 (2.9%). So over 50% use the latest stable (or beta) versions of these browsers.
As for your other question--"How can you tell your end users that they will need to upgrade their browser to use the latest version of your website without a huge outcry?"--you must understand (i) the factors motivating people to upgrade, and (ii) the factors inhibiting people from upgrading; then you must use these factors to bolster your appeal to your end-users.
Motivators
What rewards do end-users get by upgrading? Skimming Microsoft's IE8 marketing materials, these are the motivators they stressed most:
- Appeals to Efficiency/Laziness:
- Faster surfing (i.e., you will gain more free-time if you switch)
- You can accomplish more work with fewer clicks, because of a more intuitive design. IE7 had put certain buttons in strange places, etc. (I.e., you will lose less effort [as measured in clicks] if you upgrade).
- Appeals to Security/Fear:
- SmartScreen protects you from malicious software (i.e., you will lose safety if you don't upgrade).
- Compatibility View allows you to view older pages correctly just as the website’s designers intended (i.e., you won't lose anything if you upgrade).
So motivators boil down to what the end-user will gain by upgrading (or lose if they don't upgrade). These things must be important to the end-user: Time, effort, financial security, compatibility, etc.
Reinforcers
Reinforcers aren't rewards, but they help increase the rate of adopting the desired behavior. Here's an example: Your web site can detect old versions of browsers, and direct users to download and install the latest versions by providing links and motivators.
Inhibitors
- Nuisance (cost in terms of time and effort) to upgrade
- Nuisance of learning something new
- New versions are inevitably buggy and suffer from incompatibilities that haven't yet been discovered
You must anticipate these arguments, and develop effective counter-arguments:
- There is a risk/reward trade-off, and the rewards outweigh these risks.
- New versions of browsers are fully supported, and bugs will be worked out. By contrast, older versions aren't well supported; and the oldest version have lost support entirely.
Best Answer
The best answer I can suggest is: Selenium. It is available for Chrome, Firefox, and IE. It can even generate test cases that can be automated by VSTS. You can also create a farm of browser test automation machines to execute the tests.