If you search you might find a thread with very good explanation, (all down to the physiscs of it which I don't really understand, the thread was full of numbers and formulas i recall) that shows the difference in string tension when the angle of the string changes.
but as darkhorse said, don't think there is much "real life" difference in this.
I think someone stated the main advantage of 45 angle against 90 is that the string suffers less and should last a bit more... but i might just be making this up. don't take my word for it.
Thank's jmorbita, I'll have a look.
I have this project: to turn a JTB-401 '54 style P into something inspired by Carl Radle's '68 custom Tele: adding a split coil to the stock single coil. I have a Bill Lawrence P46 to add. At the same time I want to play around a bit and turn it into something a bit more unique: reshape headstock; recess the neck into the body more; Hipshot Ultra-lite tuners; new pots and cap; and make the bridge string through (which will reposition to accommodate the neck recession) - and thought the Yamaha angle was a cool idea. Yes, I've read a lot that perhaps there is not difference in a through-body approach... but it will be a good exercise. Stock bass is a pretty dang sweet instrument for $300. Very solid.