actually both has same Webkit core engine same build. just that the browser (front end to rendering engine) is coded differently.yahoo 360 works fine on Safari 3 for Mac OS X (10.4.9) It looks like Safari 3 for Mac works better than the one on PC since they're starting from ground up on the PC while Safari for Mac is just a update with new coding.
you know you could build a browser with webkit like someone did last year
First Windows Browser Based on Apple's Webkit - OSNews.com
Webkit is open source project by Apple
The WebKit Open Source Project
See their blog there...