I think IT'S the HEIGHT of the keycaps. Look at the picture and see how deep height of the filcos (blacks) compared to the mx11800's (beige). I think the height of the filco's + the inherirant wobbliness of the cherry browns makes it less comfortable to depress the keys when struck at a less than perfect angle. Also, the top of the keys seem a bit more flat and smoother on the mx11800's than filcos...
In conclusion, I'm a weirdo keyboard fetishist who'll never get married.