I found the culprit (with the help of an experienced cloud server guy) 
There was no problem with the Arduino code nor the PHP file...
The reason was very obvious from the start (but I didn't noticed it 
)
and even before my problem went from confusing to worstly confusing...
:0
I can't get through with the ever simple first step of accessing the web server through my web server
due to the Security Group in which my AWS server was initially set.
The Security Group in AWS is the one which allows and blocks ports and firewalls in the network...
The default Security Group I was into had some restrictions and rules on ports/firewalls, thus
the problems I had in actually writing data from Arduino to the server..
A new security group with all filters disabled, was made available into my Options.
I ran a new instance of my server and used the new security group, and tried the same code and php file..
Now my browser is able to access the IP address, and insert the data from my sensor
to the cloud server...
Lesson learned: always check security groups before deploying AWS server images.. 8)