never said anything about anything being the "culprit", but obviously any fuse would have a reason to be used. Logically a fuse in a power-line is used to protect against what would happen if the power-line after the fuse would be shorted. Thats not "blaming the short" in any logical sense.
Using such fuses in series with the USB power lines is standard practice, and for what other reason would that be to prevent that a short on any USB device (or cable) would short the 5V supply, which in a normal PC could generate enough current to burn up said USB cables, and maybe burn up PCB traces on the PC's motherboard too. So its standard industry practice to have them, but the standard industry practice does not translate to a valid reason to have them on the PI, as a normal R-PI power supply doesn't have enough power to do much damage, unless a 5A laboratory power supply was used.
You could argue that the fuses could be useful if something from the outside, connected to the PI's USB ports would supply power to the R-PI's USB port, and the R-PI itself developed a short, but this is a very unlikely scenario, and most USB hubs (because these are the candidates for a device that might put power back into the USB port) are themselves reasonably lightly powered.
My remark was only made because some comments indicated that the USB fuses somehow could protect the RPI from crashing when such a short occurred, which obviously isn't true.
Routing the power from the Power input to the USB fuses around the main fuse is simply a good idea because it prevents having two fuses in series, which serves no real purpose, and adds the resistance of the to fuses together, increasing the voltage drop, and thus increases the potential for failure.
And yes, if the R-PI designer(s) would have thought of the resistance a polyfuse has, and therefore had chosen a more sensible value of perhaps 750mA, then, providing the external PSU used could cope with it would have been able to power even devices wanting more than the standard 100mA.
Perhaps their reasoning was that these ports would always be used up by a mouse and a keyboard, or if the user wanted to add more devices, a powered hub would be used, thus the ports would never have to supply more than 100mA. So they chose a fuse with a tripping point roughly 50% above that number, not realizing the implications.
I have to say I cannot blame them, as I in the far past I have made the exact same error when trying to protect the 5V power input of a device (made from 5V powered logic consuming roughly 1.5 Amp) with a 3A fuse, (glass tube kind) only to find out the device would not work with a 5V power supply because of the resistance of the fuse. I had to bridge the fuse with a wire to solve the problem, as I calculated I needed a 15A fuse to get a reasonable low resistance between the PSU and the 5V logic, and a 15A fuse wasn't a practical proposal, so I was better of having none. The original thought was that the fuse should help protect the device (together with a reverse diode, and a six volt overvoltage protector) against using the wrong power supply (one with a higher voltage than 5.0 Volt, or with a reversed polarity),
Luckily the R-PI doesn't have that problem, because the used the micro USB connector, (always used with 5V and a knows polarity) but they still use a overvoltage protection device, (D17) and a fuse, (F3) which luckily for them has a sufficiently low resistance, (because of the R-PI's much lower input current, they could use an 1.1A polyfuse with a sufficiently low cold resistance for the currents that normally run through it) although I still have a feeling it could sometimes be a factor, if for some reason the input polyfuse develops a higher than normal resistance, for example when a unusual high current has run through it recently.