the correct name is prefrence wise filling of branch intead of choice filling in iit jee and aieee because here u r filling branches prefrence wise u have only one option regarding ur choice that is ur preference choice filling means u have lot of option to chose any one of them its depand up to you but here what these people doing they ask us to fill the prefrences wise choices

so that if you dont get your higher choices because of not being under the required air for that you can atleast get one of your other choices in preference wise...

what happend in medical field that they call u ur rank wise and offerd u lot of choics which is left for you and its up to you what u preferd i mean u have lot of option as per ur rank but here no choice left after filling  the preferences

no its not like that they will give you your highest available choice to you and its up to you whether to take it or not..maybe medical people do it because they have very less people(around 1500 for aipmt) qualified for counselling and thats easy for them..but here are whole 18k people for counselling so one cant do like that...