The site is general and has no Apple content. The reason above (Safari previews) is correct and the figures are not adjusted to allow for that. From the Safari bounce rate and av. time on site, I'd say a third of the 20% may be previews. - So a better estimate may be:

Internet Explorer 47%
Chrome 18%
Safari 14%
Firefox 14%

These are the figures for visitors to a 250,000 visits a month site in the UK:

Internet Explorer 44%
Safari 20%
Chrome 17%
Firefox 13%

In any case, I'm not sure what 'choice' many visitors have. Some people get what their IT department installs, others stick with what is on (eg Mac/Safari or Windows/IE), others with what their familt IT support insists on.

If the order posted on Chilling Effects is correct you can see why Google took a broad view [my emphasis]:

Order the defendant to withdraw the articles, photographs and graphic representations of Belgian publishers of the French - and German-speaking daily press, represented by the plaintiff, from all their sites (Google News and "cache" Google or any other name within 10 days of the notification of the intervening order, under penalty of a daily fine of 1,000,000.- ? per day of delay;

http://www.chillingeffects.org/notice.cgi?sID=2160

With a decent micropayment system Google could really change the web. It's a shame this is not it. It's likely Google could blend micropayments into sites pretty well with their AJAX skills - and their infrastructure should mean that the implementation cost was marginal (for them). And search could benefit. A micropayment is a pretty good vote for a site.