Hello Sri Karunanandan,
If you are referring to the Webcasts offered from the Communities, it could be that you are not following the Communities that your colleagues are. Can you provide me an example of a Webcast that you didn't get a notification and they did?
For example we recently had a new Support Online user on-boarding webcast that was managed out this Customer Care Community. We not only posted on this Community but several Product Communities. If you were not following any of those Communities you may not have received a notification.
Regards,
Colleen