Witch -Infected wounds major hex (Ultimate magic) vs blight hex(APG).

[Endoralis]

My obvious guess being that Blight is specific to 3 types of things while Infected wounds could apply to any creature...

[Aldin]

The restriction of Blight to animals and plants (for the Con damage) is pretty significant. As a side note, Blight is removed with Remove Curse while Infected Wounds is removed with Remove Disease.