That's not really true. Pot type is a matter of preference and you can use whatever you like. The JB Jr bridge is bright so it could use a 250k pot, however a 500K pot for the Little 59 and Hotrails is just fine. If you approach the choice of pots from the standpoint of resistance you get a bit better results. Because the higher the resistance the darker the pickup and the larger the value pot. The majority of single coil sized humbuckers are above 8K resistance which puts them in humbucker territory and they work fine with 500K pots. Even single coils with high resistance like the Hot, Quarter Pounder Custom can use 500K pots.
The choice of pot has to deal with the relative amount of treble/bass you want. Lower value pots bleed more treble to ground and create a darker sound than higher value pots. It's a balancing act because if you use too low a value pot you can constrict dynamics and muffle a pickups sound, whereas too high a value will make a pickup sound bright and brittle. The right value pot should give you a good dynamic range and resonance, while smoothing out pickups sound. What that sounds like is up to you and your preferences.
If you look at it from a resistance/MV output point of view the general rule is the lower the resistance/MV output the lower value volume pot you would use. The higher the resistance/MV output the higher value pot you would use. The higher the resistance/MV output of the pickup the darker it is going to be due to frequency attenuation. Volume pots have a bigger impact on sound than tone controls because tone controls really don't much bleed treble when they're not being used. If you want to brighten up a pickups sound start with the volume before the tone controls.
