The primary software that they use is in no way compatible with Linux. They do not want to spend any money on retraining/ rehiring IT. They have a deal going with manufacturers and Microsoft. There are many other reasons why a company would opt not to use linux as well as many why they would.
because its free more secure less maintenance
Sure! Internet cafes can use Linux no problem if they so choose.
Different Linux distributions can use different GUI's some will use Gnome or KDE. Most distributions will let you choose which you want. If you have an older machine you might want to use XFCE or LXDE window managers. If you are looking for a distribution you might want to try Linux Mint it uses all of these Window Managers.
No. Those user interfaces are copyrighted. However, some distros have fairly similar interfaces that you can use instead.
Yes. All that you need to do is shrink the Windows partition so your Linux partition can fit. Then just install the Linux OS into there, and you'll be able to choose which one to boot into on startup
Linux is a monolithic kernel. Some operating systems with a microkernel use Linux as a process for providing drivers, but this is irrelevant to mainstream Linux.
Some people refers to Linux-based systems as "GNU/Linux" if they use software written fr the GNU operating system.
Almost all Linux installers will allow you to choose which disk is used when one partitions the disk (choose manual to choose which hard drive to use)
This obviously depends what platform your writing your program for, if it's for Linux/BSD/Solaris etc, use Linux. If it's for Windows guess what you use? Windows (Except in some cases using Linux is okay). If it's for... you get the point. Personally, I use Linux.
No, it is unix-based but Linux is a kernel not an operating system.Ubuntu,Linux Mint,Debian,and puppy Linux,ect. are OS's that use the Linux kernel.
No Apple products currently ship with Linux. Apple has worked on Linux in the past to create projects like MkLinux. Some projects that Apple has created, such as CUPS and Clang will run on Linux.
By dual-booting. You install them both to the same computer and choose between them at boot.