Is It Necessary To Have A Default Browser

What I am wondering, is it necessary to have one of these mentioned browsers set as default?

For several weeks somehow none of them was set as default until this afternoon, when Microsoft sent me the link for the new IE 9 Internet Explorer Platform Preview. When I download the platform preview once again IE 8 became the default browser.

If it isn’t necessary to need a default browser, could someone please advise me how to remove IE 8 from being the default browser? It appears I have forgotten how I removed it as the default browser the first time.

Again, thanks!

Ron