This deflection has always puzzled me too. When I've looked at diagrams of an Epson piezo head, the exit of the nozzle appears to be simply a hole in a ceramic or glass plate. The ink seems to be "flicked" by the piezo element, and directed by the "hole".
Based on my understanding, the deflection appears to be caused by either a damaged piezo element flicking the ink the wrong way through the "hole", or a buildup up pigment on the inside of the hole drawing the flicked ink in a new direction. If it is the damaged piezo element, I can see this being a permanent situation, and the channel not being usable anymore. (Is this condition caused by running too many clean cycles or using the printer too much with clogged nozzles, overheating the piezo element?)
If it is a buildup of pigment causing the flicked ink to be drawn in the wrong direction, I suppose if it were to sit with piezoflush for a long time it might clear. I'm hedging my bets on damaged piezo elements given that I've not heard of deflected nozzles repairing themselves.
Forgive me if my reply seems oversimplified. But, if I know the main causes this condition (overheating nozzles?), perhaps I can avoid this condition and have many great loving years with my printer.