where is the problem exactly? there is no contradiction. the specs sheet says that they both use the same CPU, which is correct. the wiki says they both use the same switch chip, which is also correct.
According to this page: http://wiki.mikrotik.com/wiki/Manual:Switch_Chip_Features , it appears that RB450G has ether1 LAN port independent on the switch chip, which not the case for RB750G. The advantage is higher troughtput from switch (ether2-5) to ether1 port on RB450G in routing or bridging mode.