What is the difference between the two besides the obvious modular cables?

Powerstream is more expensive and is a better PSU. Has higher and stronger rails and is just a better PSU all around which is why it cost more. The powerstream is more of an enthusiast PSU and the modstream is more for people that aren't real extreme, but want their rig to look good.

Modstream is more looks than preformance, its aimed at the aesthetics market more than at the preformance market. T

Yep

But my modstream is wicked nonetheless! Very strong on all rails, but stupid to only come with one floppy power connector