Bad, bad, Apple.
The above linked blog gives some examples about how Apple's Safari browser achieves it's 'OS X-ish' look in Windows. It does this by way of some Safari specific CSS attributes. These custom attributes allow Safari to do some custom 'rounded OS X-ish' button styles on standard web pages - at least ones that are running in Safari.
I really hate when browser developers like Apple or Microsoft do custom stuff like this! Web site developers have a hard enough time making web sites that work in all browsers. When there are tons of custom features that are specific to certain browsers, it just makes things all that more difficult.
Get with the program, Apple. Why can't you simply use standard CSS for this stuff rather than yet another non-standard addition! Sheesh.