It is a "new" product. You can have both versions of PS installed on your system at the same time, but you cannot update from one to another. Why Adobe did it this way I can't say.
Photoshop CC (2014) is an "upgrade" not an "update". The changes in CC (2014) go beyond the scope of application patching and required a whole new version (version 15) to be installed. Also, for certain backwards compatibility issues, Adobe almost encourages you to keep Photoshop CC in addition to installing Photoshop CC (2014).
I won't defend Adobe's decision to add a year to the CC as a way of distinguishing an upgrade vs an update and I don't think they've explained it all that well, but if you understands what's going on with installing a whole new app vs a simple update, what they did makes sense.