Regarding JEE, AIEEE, etc. - it's not so much of a selection system as it is an elimination system.
I have also said before on this very forum that all these entrance exams are geared and meant for "average students" with little to no knowledge of technical subjects. The people who are technically inclined from the start are still small in number in India. Given the aspirations of the youth as well as their parents, I guess it is justified why the selection was decided to be made on the basis of PCM/PCB - to give all students a fair ground to compete on since everybody would know PCM but not everybody will be knowing stuff like ion implantation, die fabrication, Web 2.0, etc.
That still doesn't make it right though.
As far as syllabi go, if you are studying in a decent university like Jadavpur (for example), you will be studying exactly the same thing as the IITs for the most part. So don't worry about syllabus.
As for CS/CE syllabus, you'd be surprised how many people still don't have a computer at home, or don't know how to use it. But since they did get admission based on PCM, something has to be done to make these people competent in computer handling. That's why the syllabi focuses on basics only, otherwise you'd be surprised just how many people will fail
It's a necessary evil caused by the elimination system.