Why bluetooth is not included in windows 7

What do you mean? Windows 7 has native drivers for many bluetooth adapters. Mine loaded up in about 10 seconds. No driver hunting required.

Going by the type of questions I've come across recently on this and other forums, I get the impression they think if they have a bluetooth device it connects to the computer all by itself without the need of a receiver, other then the driver.
The makers of these devices are partly to blame as they don't make it clear that a dongle is needed.
Here is an example from Nokia:
"The Get Connected wizard helps you to connect your mobile phone to a PC. After you have completed the wizard steps, you have established a connection between your phone and the PC, and can start using Nokia PC Suite applications.

The Get Connected wizard consists of the following steps:

Select which connection type to use when connecting the phone to the PC. This can be cable, infrared or Bluetooth wireless technology.

Establish and configure the connection"

As you can see no mention that a Bluetooth dongle is needed at the PC end.

Point taken. Now that I think about it, I do wish the packaging would specify that a receiver was needed. It didn't say anything about needing one on the bluetooth headset I got for my phone either, which following your line of thinking, would have been handy if I didn't know about it. I connect that headset to my PC to talk through Skype as well.

Many laptops have bluetooth built-in, but not very many desktops come equipped with it. I've seen a few Dells that people have ordered with bluetooth keyboards and mice, but that's about it. (These do have a USB bluetooth dongle).

I agree... people need to be made more aware that bluetooth is more than just software... there has to be hardware behind it.