To get the intonation bang-on right, some string gauges NEED to be different lengths. When you fret the strings, you are pulling them out of a straight line and therefore the tension in the string increases, and this needs to be compensated for by making the string length a little longer for it to remain in tune..hence "compensated" bridges. The point of the string where you strike a harmonic is exactly halfway along the string - it's fundamental physics, BUT, as soon as you fret the guitar, you are introducing another variable, that of bending the string out of a straight line and minutely increasing the tension on it..but just enough to pull it a tiny bit sharp.
How much compensation is needed is determined by the scale length, string gauge and the tension in the string - the difference in the way plain and wound strings react can be seen on a lot of 6 string guitar bridges where the saddle position or break point over the saddle is markedly different between the plain and wound strings. Some guitar makers traditionally don't worry too much about the issue - classical Spanish guitars and resonator guitars have straight-across bridge saddles (though you can tweak a reso by turning the biscuit or spider at an angle) .
The whole issue of string compensation is a compromise, (as indeed are modern tuning and fretting conventions) but it's the best compromise people have figured out. If you are playing slide only, then it's not really an issue . By the way, I did see on one of those photos of that shortbread tin guitar, the saddle was angled the wrong way, and by a huge amount.
If you really want to get into this, look up "equal temperament" and "just intonation" you'll find out the whole issue of conventional musical intervals and tuning is perhaps more complicated than you may imagine.