NO, it is never like that. The total students that are part of the merit list they all don't get the admission as for example in case of the JOSAA counselling there are about 11000 seats in the IITs but the result for the JEE Advanced gave more than 30,000 in the merit list. This just doesn't mean that they all will get a seat. This technique is just a precaution from the side of the colleges to ensure that all the seats get filled in cases when some of the students from within the merit lists don't wish to take the admission in those institutes.

Hope it Helps... Good Luck!