It’s common knowledge that a lot of (most) web/graphic designers uses a Mac. Consequently, they tend to use Mac fonts in their style sheets as their first options (at least quite often). Unfortunately fonts like Lucida Grande, Lucida sans etc. are NOT included in the normal Windows package.
Well know you can get it too! After a bit of googeling I finally found the best emulations of all the OS X system fonts. If you just want to get the emulated Mac Lucida fonts go here.