It might also help bring some of those titles to Linux. Since OS/X is *nix based, having it on Intel architecture should make it easier to port those applications to Linux.
OS X is based on FreeBSD, not Unix.
Fat chance. Not because it's technically difficult, as you infer, but because the vendors aren't convinced many in the Linux crowd are willing to pay anything for their software.
I'm not so sure. Writing a graphical-based app for OS X is way different than writing for Linux. For Mac you use Cocoa with the Mac windowing APIs, and for Linux you usually use X or one of the other GUIs. Going the other way is easier, since the Mac can run X. But even that isn't the greatest solution, as OpenOffice.org found out.