master/slave doesn't refer to triggering indiv. notes from one machine 2 another (and the mpc can both send and receive notes, its true. so the micron thing will work.)
it refers to having 2 machines that are each playing back from their own sequencers, and you want the tempo to line up, so you use 'midi clock' to send timing signals from one (master) to the other (slave).
and, the mpc can be a master, but only using 'midi clock' not using 'midi time code' (not the same). for instance, mpc is master to my machinedrum, works fine. the reason it doesn't work with cubase is more to do with the way they programmed cubase.
also, i agree w/ everyone that using cubase as master basically works, and u probably wont notice problems... but, i do have a feeling that the timin won't be quite as tight.
the reason i think this is that pc midi interfaces usually have a lot of jitter (random deviation) in the output:: i notice this if i use my machinedrum as slave to pc:: u can look at the tempo display, and it's bouncing up and down.
i have also read articles about this jitter, and even measured it one time for part of a school project (dont ask

)
now it is true that there are some midi interfaces that use a better method to interact with cubase (time stamping) and are going to be better than your run of the mill midisport or whatever. in that case u can probly get really tight timing out of cubase.