and Assessment Centers are just organized for top business schools as well... ah, just such a pain...

hola. Employers worldwide view the assessment centre as an excellent predictor of job performance. I'd like to point out three main points: they can test you in all sort of ways; they have the luxury of observing your behaviour and social skills; they can interact with you in a way that simply cannot be done during the course of an interview. These are very good things from an employer point of view: they can be confident that they will have the perfect person for the job at the end of the process.

I noticed the same thing. I applied for ICAP, Barcap and HSBC internships and everyone has an assessment centre as final step of the recruiting process. I think this is the best way to see how you exactly work!