Much like your BTC, if you do not have possession of it you do not really own it.
Go back a bit over a year, and how many of the hashing power by the GH/s bonds are still around? GigaVPS is still paying dividends, but retroactive forced an at-your-cost verification process and changed the perpetual bonds into single year bonds. The majority of the rest took the opportunity of GLBSE closing to cut and run.
There are so many things that can go wrong with these scenarios from straight fraud to government regulation changes to the medium of exchange shutting down that comparing having hardware in hand vs having the promise of someone else continuing perpetual payments and not screwing you/quitting/getting hit by a bus on a straight $/GH/s basis isn't a proper comparison.
I totally agree, it's a risky approach. I like to diversify my portfolio. Personally I will definitively keep my own hardware + do some trading on their service.
They own like 19% of the total network power, so I guess the risk is somewhat limited, they must have some big money behind them.
What I like with their service is "infinite compound interest". I can buy more power as soon as I'm paid for a block.