i saw a few JC's combination just now,i dun really
understand,why do JCs allow students to take science at H2 level
with combined science and u nid a math to take H2 math??
issit bcos the "jump" from combine science to h2 science can be
coped,and the jump for a non amath student to H2 maths is even
bigger and is very hard,hence nid a math as an advantage?
This....you will have to ask the policy makers sitting in MOE
HQ. 
Look on the bright side, there are JCs which makes exceptions
though.