I do not understand why everyone is fixated on the initial 100 Mh/s estimate. It is an estimate of the initial hashrate per share and will grow just as Asicminer's does/has albeit probably not at the same rate. When I first looked into Asicminer everyone was screaming about how only an idiot would buy into something that gets you around 56 Mh/s per share (if my memory serves me correctly). I'm sure glad I was one of those idiots.
Difference is with ASICMINER you owned shares - and were entitled to growth in hardware.
Here it's neither a bond nor a share - and the contract gives you no rights to anything other than the 100 MH/s. If he wanted to take a defined percentage of profit then he could have written the contract to do that. He didn't - so obviously he doesn't want a fixed percentage of profit. Relying on anything the contract doesn't grant you is just terrible practice. When someone writes a contract giving very little assume that's all you get. If you wanted to rely on charity then we could skip the whole securities thing, just send him BTC direct and get back whatever he felt like giving.