The curves are currently part of the "look and feel" of Node-RED, and are indeed somewhat hardcoded (inside view.js) . Indeed once upon a time we didn't have a snap-to-grid so it was all a lot more free form. Just because other tools do force things to 90 degrees doesn't necessarily make it right :-)... but yes I can see it does make sense for circuit diagrams where you can overlap wires in a bus - though they also sometimes have jumps and junctions to indicate whether they should connect or not.
Note, Node-RED wires do not have properties (they are just an array of endpoints on nodes) so saving things like how many pixels to go before turning 90 degrees etc (ie the geometry) would need serious thinking about, if it isn't going to break things.
There was also this recent thread about wires - [Feature Request]Do nodes or lines know if they are above/below each other?.
