Is everyone violating ICAI Act regulations?

Yes you are right, as per rules, during articleship period we can pursue only one additional course.  And obviously any one pursuing more than one, dont have permission from ICAI.  If at the time of applying for membership, institute dont have any information regarding additional course then it wont create any problem.  I have heard that In most of the cases problem arises when you go for campus placements of ICAI.  There you would like to mention all your courses in your resume, however then ICAI can create troubles for you. 

So unless you are caught, you can pursue as many courses as you want just like others are doing.  But remember it will be against the rules of ICAI.