I remember in the introduction text how it described Earth settling down and being mostly at peace before the alien attack, wars calming down, etc. (Not that that's likely to happen, but that's a different topic.) Given this assumption and idea that everything is calm and peaceful before the Mumbai attack I'd imagine one could argue that because the Earth is all in harmony and everything that weapons technology isn't as important anymore, military forces are reduced or even virtually non-existent because they aren't needed anymore, and when the aliens arrive that the player's forces, a secret organization, are forced to un-bury and "dust off" old technology to start with (before research teams come up with the laser weapons, bolter rifle, etc.).
Along with that idea, perhaps the starting weapons could actually be much less than 80 years in the future, but still be the best available at the start of the game because, again, the technology was slowed down and put aside for years afterward, with world peace and everything.
