They may 'cut corners' by getting a better price on the pots by not having very high tolerances on their pots. For example, with a 30% tolerance, they'll sell you a "500K" pot that reads 350K...hey, it's 'within tolderance'...
You get what you pay for.
And you'll still have to enlarge the holes in your guitar if you bought a CTS pot from allparts. A few moments with an Exacto knife isn't exactly "routing"...
