Any website operated by or for the government or other public body should be written to web standards so they can be viewed in any browser.
Example being this site – Voting only works in IE from what I can tell.
I'm not sure how it could be enforced … maybe a name and shame website.
There is bound to be some time where a feature is created that can only work on certain devices which is fair enough, but it should state clearly that this is the case.
Why is this idea important?
We access the web in many different ways and on many different devices.
Universal access can be achieved if it's written to standards so that everyone can find information or have their voice heard & opinion counted.
This can then also help the disabled eg. if a browser speaks the site to the blind – if the site is badly done it may not work and deny them access.