Edit: I just wanted to add that Dash accomplishes this while still using Proof of Work to secure the blockchain (avoiding PoS) which is an important plus in my opinion. And only uses stake holdings for governance purposes but only attached to full node operation which I think is a superior way of doing it than just voting based on coin holdings without a direct network responsibility like masternodes.
+100
Proof of work is very important. It is the key feature that gave Bitcoin its legitimacy, and was a master stroke from Satoshi. Proof of work invites participation (and competition) not seen in other currencies. Just look at the Dash mining subforum and all its activity. We have ASICs now! I'm still pinching myself that we have friggin ASICs from different vendors.
That is where it gets serious, because real world capital investments have been made to mine just X11 currencies. ASICs provide security AND legitimacy. The proof of stake coins do not have a good track record. NXT and Peercoin are the poster children, having fallen out of the top 5, and struggling to stay relevant.
Now I have to get back on reddit and (politely) correct some of the noobs who think that masternodes are just nodes doing proof of stake. Nope, it's proof of service.