I observed that MacOSX finder does not have a Cut option (or shortcut Command+X) to move the contents. Is there a reason for removing this option? Does it improve usability in any way?
Actually Mac OS X 10.7 does have Cut & Paste option:
Command + C to copy then Command + Option + V to paste. The original source file will disappear.
But this command isn't listed under the Edit menu. So it's still a secret to many people.
Mac does support Copy as well as Cut as explained above. The only difference is how they are perceived.
On Windows and other environments, users need to decide before taking an action whether they want to copy content or move content. Paste is a simple activity that depends on the previous action taken. It has a usability flaw which is evident in an example where user chose to copy - now if he wants to move content instead of copy, they have to go back and cut the content to be able to move it.
Unlike this action based task-flow, Mac has taken the route of cognition based task flow. They do not have separate action keys for copy and cut, rather they are more task based - copy and move. So a single action to copy brings the item to your clipboard (think of it as picking the item from your container). Now while taking the action of putting it into some other container, the user can decide whether he wants to drop that item in new container or simple place a copy of the picked item in new container while putting the original item back in its parent container.
This has made Macs more usable since now users dont have to decide at the time to selecting an item whether they want to copy or move. Rather while dropping the item they have the choice to make. Thereby users dont have to go back and forth to change their decision. This is specially true because typically files lie in different folders and if one changes their mind between copy and move, they have to do lot of traversing among the source and destination folders.
So Mac has implemented Copy and Move in more understandable format whereas other OSs have taken the route of forcing users to make that choice first by making copy and move explicit by using actions like copy and paste.
There are 2 things that works against the usage style of Mac though: 1. The action to put into clipboard is called copy which might be confusing as Copy usually means creating a copy of the item. So the actual usage is not same as what the label would mean. 2. Move functionality is hidden in keyboard shortcuts and not evident to the users. Only advanced users or users who have taken the pain to learn the keyboard shortcuts for various tasks on Mac would know that such a functionality exists. A beginner user would simply assume that such an important functionality is completely missing on Mac. Infact, the option to Move doesn't even exists in Edit menu of Finder thereby hiding it completely from the user.