just because you do not use it in indonesia does not mean, it would not be important.
just think of free frequencies when having a big wisp-net, when you connect everything at 2,4ghz there is not really room for the customer to build up his own wlan at home.
and i think to accomplish 5ghz on those rb411r we are talking about programming the eeprom to the right values and using a 5xxx-atheros chipset, both not really challenging tasks as they have been done before by mt several times.
it more looks like a marketing issue, why putting a competitor for a rb411 with a r52 for a lower price with one more mini-pci-slot on the market than simply gain more money by selling the other combination? mt has always the advantage that they fix the customer to their software and if there is no option in other hardware, they have to buy a more expensive product.
if it is like that (which i honestly think) then its sad, but perhaps normis says sth about that and explains why it has no 5ghz, it can't really be a hardware-design-problem.