I don't know much about electribes, they are a synth, sequencer and drum machine in one basically no? if so the two are pretty different beasts. I imagine if that's the case the ielectribe is much closer to the original hardware than impc would be.
The MPC is not just for sampling, it's most powerful as a midi sequencer. So if you are a cool guy like potetoboy above and have a army of awesome synthesizers or any midi instruments at all, you can use the MPC to control all of them
I have a midi keyboard going into my MPC and the midi outputs go out to my synths so I can control and record any of them independently with the one keyboard and then play them back all at once if I wish.
iMPC on the otherhand is mostly a basic version of just the sampling side of the MPC. I don't wanna quite say it's just a toy or just for fun as I imagine it's good enough that someone with some talent and alot of patience could make good music with it, but mostly I think it's something to just bang out ideas with on the go, it just doesn't have the features for chopping and layering samples to compare to a real MPC, but it's cool that it has a pretty accurate MPC style workflow.
as far as mashing pads goes... that part is pretty accurate
sure you can step sequence on a MPC too, but I am all about mashing pads.
forgive the rambling, what I am getting at is a MPC is like a workstation you will use to bring everything together, a electribe is more of a instrument one might even use along side the MPC.