HX750 and HX850 have been out for a while. You're right. There have since been advances in technology for consumer computer power supplies, but details of the topological differences, new parts, etc. are probably not that interesting to consumers. These old power supplies have quite excellent performance anyway, so who cares?
The main developments that are more visible to consumers, would be the push for higher efficiency—80 plus gold and platinum. That just means that a little less power is wasted as heat. Also, more units these days have a fanless mode at low loads. Corsair AX650 through AX850 are examples of these things. They're not any better than the HX750, except having the higher efficiency, quieter operation, and full modular cabling.
But actually, Corsair actually is updating the HX series very soon...with slightly better or similar performance, 80 plus gold efficiency, and a fanless mode at low loads.
You can find reviews of the new HX series at the usual suspects:
http://www.techpowerup.com/reviews/Corsair/HX850_V2/
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=299
http://www.hardwaresecrets.com/article/Corsair-HX850-Gold-Power-Supply-Review/1602
http://www.kitguru.net/components/power-supplies/zardon/corsair-hx850-gold-professional-series-power-supply-review/
haha
